Spring shot peening

Shot peening is generally used in the processing of automobile spring steel plates. It is to reduce the plastic deformation of the processed material.
Shot peening is divided into general shot peening and stress shot peening. In general processing, the steel plate is in a free state, and high-speed steel shot is used to hit the inside of the steel plate to generate pre-compression stress on the surface. To reduce the tensile stress on the surface of the steel plate during work, increase Service life. Stress shot peening is to pre-bend the steel plate under a certain force, and then perform shot peening.
Shot peening is a cold working method that accelerates the pellets with a proper acceleration device and sprays them to the workpiece in a proper way.
Shot peening
Shot peening is used to plastically deform the surface layer and form a strained layer, in which the transformation ratio of the structure and residual stress occurs. Properly controlling these changes in the strain layer can improve the fatigue fracture resistance and stress corrosion cracking resistance of the parts.
Springs are one of the earliest parts in the production of shot peening, especially those compression coil springs, leaf springs and torsion bar springs that are subject to cyclic loads and are prone to fatigue damage. They must be shot peened.
Shot peening is arranged after spring forming and heat treatment. Using small metal balls or metal particles, sprayed on the surface of the spring countless times at a speed of tens of meters per second to produce many small pressure pits, which are uniformly bulging, covering the surface layer of the spring and on the surface layer It produces work hardening, and at the same time it can reduce or eliminate the harmful effects of spring surface defects (such as small cracks, uneven gaps and decarburized layers, etc.), thereby effectively improving the fatigue life of the spring.
Pay attention to the shot peening operation: ①Select the type and specification of the shot correctly, avoid using sharp-edged shots to damage the surface of the spring; ②Select a shot blasting machine reasonably, requiring high injection speed; ③The shot blasting time is required when the conditions are possible Properly longer, so that although the strength of the spring cannot continue to be improved, it can increase the coverage of shot peening and also increase the fatigue life.
The ratio between the area occupied by the bullet marks and the area required for shot peening on the specified parts of the surface of the shot peened part is called the surface coverage. The surface coverage is expressed as a percentage.

Spring-the process of cold forming

There are two types of spring manufacturing methods: cold-rolling method and hot-rolling method. Under normal circumstances, the spring wire with a diameter of less than 8 mm generally uses the cold coil method, and the spring wire with a diameter of more than 8 mm uses the hot coil method. Some springs need to be subjected to strong pressure or shot peening after they are made to improve the load-bearing capacity of the springs.
One-time automation capability of the spring cold forming process. The cold forming machine has now developed to 12 jaws. The steel wire in the range of (0.3-14)mm can basically be formed at one time by the 8-jaw forming machine. The current development direction of forming process equipment:
①Improve the forming speed, the main development trend is to increase the forming speed of the equipment, that is, the production efficiency; ②Improve the durability of the equipment by improving the precision of equipment parts and strengthening the effect of heat treatment; ③Increase the length sensor and laser rangefinder to form CNC The machine performs automatic closed-loop control of the manufacturing process.
Cold forming process range capability. At present, the maximum specification of large wire diameter spring coiling machine can reach 20mm, 2000MPa, and the winding ratio is 5. The cold forming process of variable diameter or equal diameter material Minic-Block spring and eccentric spring still has limitations.
When using materials that do not need to be quenched and tempered to make a spring after forming, the process is
Spiral compression spring: coiling, stress relief annealing, grinding on both ends, (shot blasting), (aligning), (stress relief annealing), standing or pressure treatment, inspection, surface anticorrosion treatment, packaging.
Spiral tension spring: coiling, stress relief annealing, hook and loop production, (tail trimming), stress relief annealing, standing treatment, inspection, surface anticorrosion treatment, packaging.
Spiral torsion spring: coiling, stress relief annealing, torsion arm making, tail trimming, stress relief annealing, standing treatment, inspection, surface anticorrosion treatment, packaging.
When using materials that need to be quenched and tempered after forming, the main difference from the above process is that they need to be quenched and tempered after forming. Sometimes the spring end processing needs to be normalized.
Generally speaking, spring manufacturing materials should have high elastic limit, fatigue limit, impact toughness and good heat treatment performance, etc. Commonly used are carbon spring steel, alloy spring steel, stainless spring steel, copper alloy, nickel alloy and rubber Wait.

Heat treatment process of long flat steel wire spiral spring

At present, long flat wire coil springs are manufactured abroad by using oil-quenched and tempered steel wire to be wound into shape and then tempered at low temperature to eliminate winding stress. In China, there is no professional factory that produces this kind of springs, so most of these special-shaped cross-section steel wires are rolled or drawn from round steel wires. It is very difficult to quench and temper after winding into springs. . After a lot of research and experimentation, we explored the resistance heating and quenching process of this long spring, and achieved preliminary results. The results of the experiment are:
1. Test equipment and results
The instruments and equipment used in the test are:
(1) One ZUDG—253 salt bath furnace transformer;
(2) A set of fixing devices for the exhausted edge of spring heating and quenching;
(3) One cooling water tank;
(4) One WGG2-302 optical pyrometer, one IR-1200 infrared measuring instrument; one stopwatch.
The quenching heating time is determined according to the resistance heating is the internal heat source heating, and the temperature is a function of time. This test uses a stopwatch, optical pyrometer and infrared thermometer to measure the continuous heating time that the specimen can reach different temperatures under certain electrical parameters. , To determine the quenching heating time. The selection of quenching medium was tested according to the three quenching mediums of water and oil polyvinyl alcohol. From the test results, these three quenching media can meet the requirements of hardness and hardenability, but the water-quenched specimens are obviously brittle, and the oil pollution is large and easy to catch fire. After a large number of experiments and comparisons, it is more appropriate to choose a polyvinyl alcohol quenching agent with a concentration of 0.5%.
2. Determination of resistance heating process plan and equipment design
According to the longer characteristics and technical requirements of this spring, we compared the following three process options, namely flame quenching, high frequency quenching and resistance heating quenching. After analysis and comparison, we believe that although the resistance heating quenching program also has certain technical difficulties, The biggest feature is professional equipment that does not require the spring to rotate during heating and does not spray coolant. Therefore, the resistance heating quenching method is determined to be tested. We deduced the function of temperature change over time on the basis of heat and electricity, and in turn deduced the change law of electric energy into thermal energy and radiant heat during resistance heating process, as the reference basis for determining the parameters of resistance heating workpiece. Since the derivation is long and does not belong to the main content of this article, it is omitted here and only a brief introduction to equipment selection.
Afterwards, our experimental results analyzed that resistance heating has a higher heating rate, which can refine the austenite grains when the steel is heated. When the heating time is properly controlled, generally there will be no overheating. For resistance heating, time is very sensitive to temperature, so the material and cross-sectional dimensions are required to be uniform. On the whole, the resistance method has a fast heating speed and proper time control will not cause overheating. The relationship between oil quenching hardness and heating time is known: Although the hardness requirement can be achieved by heating for 1.5 minutes under stable electrical parameters, but taking into account the factor that the inner side of the coil is thicker than the outer side during winding, the heating time is extended 2 minutes is more appropriate.

Common problems in die casting mold production

The industrialization process of modern society is developing faster and faster. In our country, motorcycles, automobiles, home appliances and other industries are developing very rapidly, and the appearance of products in these industries is also increasing. In addition to appearances that must keep up with product performance, aesthetics gradually occupy a large market.
The appearance of these industrial products is inseparable from molds. With the development of industry, the competitive factors in the industrial market have become more and more fierce. Mold manufacturers must produce molds with the fastest speed, the lowest cost, and the highest quality. In the die casting process of mold production, there are always some production technical problems. To sum up, it mainly appears in the following two aspects:
1. Why do aluminum die castings have black spots when they are polished?
There are several reasons for this situation. It may be silica or the formation of alumina. The solution is simple: use fresh aluminum ingots. But the biggest possibility is from the release agent. It may be that we sprayed too much release agent. It is also possible that the organic content of the release agent is too high. Some of these organic substances are reduced to carbon at the temperature of hot-melting aluminum, and some become organic macromolecular polymers. The mixture of these carbon molecules and polymers is contained in the surface layer when the aluminum casting is formed, and becomes the black spot we see. We can reduce the concentration of spraying agent, switch to another spraying agent, or increase the blowing time after spraying. To reduce the formation of carbon elements and prevent the accumulation of macromolecular polymers.
2. Why can’t the machining allowance in the aluminum die-casting hole exceed 0.25mm?
In order to make die casting more perfect, humans have added a lot of silicon (SI) to the aluminum alloy used for die casting. When the aluminum alloy condenses in the mold, the silicon will float on the surface, forming a thin silicon film. This silicon film is very hard and very wear-resistant. Some OEM designers use this feature. The inner surface of the die-casting hole is directly counted as the bearing surface. This silicon surface layer is generally only 0.2 to 0.9mm. Too much processing will shorten the life of this bearing surface.
In the die-casting process of mold production, we must be careful, so that every detail does not go wrong in order to create a beautiful mold. Only with the use of advanced management methods and integrated manufacturing technology, mold manufacturers can remain invincible in the fierce market competition.

Protection against corrosion

Rust is the most important degradation phenomenon of metal substances. At the beginning of the degradation process, the beauty of the metal fastener may be lost, and then the function of the parts may be lost, and the fastening coupling must be replaced. In fact, the appearance and functionality of bolts are very important, because in addition to the mechanical properties required by the application, general bolts must also have good corrosion resistance, and must be beautiful in most mechanical components. Appearance.
1. The rust phenomenon appears in different forms.
The corrosion of fasteners in general is the same degree of damage to the metal surface. Other cases may be local rusting. In this case, we observe that the metal is oxidized in the small anode area, but there is no change in the metal surface in the large cathode area.
2. Types of corrosion
The first is uniform rust. This kind of rust phenomenon spreads over the entire fastener tissue surface and continues to produce metal reduction. This is the most common corrosion process. This corrosion does not cause too much danger and is easy to detect in advance.
Secondly, it is the phenomenon of local corrosion that is dangerous. Pinhole corrosion. In this case, it can be observed that local erosion will lead to material perforation. The anode area is very small, and the cathode area without any changes on the surface is rather large. This phenomenon often occurs in stainless steel, nickel steel and aluminum fasteners. Electric rotary rust. As far as fasteners are used, the damage caused by electro-rotating corrosion is very serious. Electro-rotation corrosion may occur in the joining of any two types of fasteners of different metal materials; the reason is that one of the metals has high activity and is easier to cause chemical reactions, so the corrosion rate increases, while the other metal has low activity and it is difficult to cause reactions. While the corrosion rate is reduced, the connection structure causes a reaction in the cathode direction. This phenomenon is even more pronounced when the electrochemical reactions of the two metals are quite different. If carbon steel is matched with stainless steel fasteners, the corrosion rate of steel parts will increase. When screws are connected, they are actually used to join two or more components. In order to avoid electro-rotating corrosion, when joining parts, the same joining materials or materials with similar electrochemical reactions should be specified.
Electro-rotation corrosion form or reaction of various metals in seawater
Form Metal Material
Inert or reactive toward the cathode
Stainless steel 18-8 type grades
Stainless steel (including 11%-30% chromium) series
nickel
Bronze (copper tin alloy)
Brass (copper-zinc alloy)
cast iron
steel
Active or react towards the anode
cadmium
aluminum
Zinc
Magnesium or magnesium alloy
Generally, fastener coatings are divided into two types. With the phosphate layer as the base, painting can increase the corrosion resistance of the fastener surface. The electrolytic galvanized layer is used as a barrier protection, and when the paint is bad and the electro-rotating rust phenomenon starts, the zinc material is used as the anode material, and the steel is used as the cathode material, which can avoid the danger of rust. Type of protection a. Electro-galvanized layer
The electro-galvanized layer is a typical anode plating layer. When corrosion occurs, the anode is preferentially dissolved to protect the base material. Limited by the thickness of its coating of 8-15μm, after chromate passivation treatment, its anti-corrosion performance is greatly improved, can withstand the 48-96h neutral salt spray test, and can be used for neutral outdoor protection. Zn-Ni, Zn-Fe, Zn-Co electroplated layers developed in recent years, especially Zn-Ni, Zn-Co electroplated layers, when the Ni content in the coating is 6%-10% or the Co content is 0.4%-1.0 %, after passivation of the 5-8μm coating, excellent anti-corrosion effect can be obtained, and it can resist the neutral salt spray test for more than 720h.
b. Non-electroplated zinc layer
The non-electrogalvanized layer mainly includes hot-dip galvanized layer, mechanical galvanized layer and Dacromet coating.
Hot-dip plating is formed by the natural adhesion of molten metal on the surface of metal fasteners to form a thin film, which is characterized by a thick coating. Mechanical plating uses the mechanical action of the small spherical object and the coating metal powder to rotate and collide in the aqueous solution to make the coating metal form a thin film. Its characteristic is that the coating is generally a composite film with good corrosion resistance. Dacromet coating is formed by sintering flake metal powder, organic matter and additives at about 300℃ to form a film. Its characteristic is that the film has good corrosion resistance.

Comparison of Fastener Pre-heat Treatment Normalizing and Annealing Process

Green manufacturing is an important strategy for the sustainable development of the machinery manufacturing industry. Normalizing and annealing in the pre-heat treatment of fasteners are the two most commonly used processes, accounting for about 30% of the heat treatment of fasteners. Although these two process methods have their own different characteristics in process, they can achieve the same (or similar) process goals when dealing with low carbon steel or medium carbon steel materials.
According to GB/T16923-1997 “Normalizing and Annealing of Steel Parts”, it can be seen that the normalizing and annealing process methods are divided into a variety of sub-categories. Among them, normalizing and incomplete annealing, isothermal annealing process processing objects, technical requirements Most identical (or similar).
1. Function
According to the low-carbon steel or medium-carbon steel used in the fasteners, normalizing is to heat the steel to 30~70℃ above Ac3, and then air-cooled or air-cooled to room temperature; incomplete annealing or isothermal annealing is to heat the steel to Ac1 is above 30~50℃, after holding for a certain period of time, it is cooled to a certain temperature with the furnace and then air cooled to room temperature. They are similar or similar in that they can treat medium carbon steel and low carbon steel, and the metallographic structure obtained by the treatment is ferrite + pearlite, which can be used as a preliminary heat treatment or final heat treatment under certain circumstances. So as to achieve the purpose of refining the structure, improving the mechanical properties and cutting performance, and eliminating internal stress.
2. Comparison of process characteristics
a. The grains after normalizing are smaller than the annealed ones, and more pearlite is obtained, and the mechanical properties are slightly higher than that of annealing;
b. Normalizing parts are often charged into the furnace, the heating temperature is generally slightly higher than that of annealing, and the holding time is shorter than that of annealing;
c. Normalizing can eliminate the network structure of carbides, but annealing cannot;
d. Normalizing treatment of carbon steel with lower carbon content is better than annealing, on the contrary, annealing is better than normalizing.
3. Process cost
The comparison between normalizing and annealing mainly exists in the power consumption of resources, the difference in heat preservation and cooling in time, and the corresponding cost difference.
The energy cost is 0.542Kw.h.Kg for normalizing and 0.580Kw.h.Kg for the domestic heat treatment industry evaluation unit consumption value, and the industrial electricity cost is calculated at 0.70 yuan/Kw.h. The average cost of annealing power is 0.03 yuan. /Kg.
The labor cost is about 1 yuan/Kg according to the lowest price of normalizing processing in various places in China. The labor cost of the normalizing process is about 0.32 yuan/Kg, and the labor cost of the annealing process is about 0.35 yuan/Kg, and the difference is 0.03 yuan. /Kg or so.
The price difference between normalizing and annealing heat treatment in the same area in China is about 0.2 yuan/Kg. In fact, after a specific analysis of the price difference, it can be known that the price difference is still based on the traditional heating method and the larger production batches.
4. Process evaluation
When the requirements of manufacturing fasteners and processing technology are basically the same, the normalizing process is more green than the annealing process, which is mainly reflected in the energy consumption and processing man-hours.
Low temperature annealing (stress relief annealing): heating temperature Ac1 carbon steel 550~650℃, eliminate the internal stress in the upsetting and cutting process, and make it reach a stable state.
Recrystallization annealing: heating temperature TR+150~250℃, holding time 0.5~1h, air cooling, recovering recrystallization process occurs, making deformed grains into small equiaxed grains, eliminating cold work hardening effect and internal stress. The annealing temperature for recrystallization of low carbon steel is 600~650℃ and the hardness is in the range of 75~90HRB.
Incomplete annealing: heating temperature Ac1+30~50℃, carbon steel is generally between 700~750℃, to refine grain, reduce hardness, improve plasticity and remove internal stress.
Spheroidizing annealing: The heating temperature is slightly higher than Ac1, and then slowly cooled to less than 500℃ air cooling after long-term heat preservation to spheroidize the carbides and reduce the hardness to improve the cold upsetting performance.
Normalizing: Low-carbon and medium-carbon steel heating temperature Ac3+ (50~70℃), low-carbon steel improves hardness, which is good for cutting, medium-carbon steel refines grains, and uniformly organizes stress relief.
Applications:
For example: 20# steel three-point welded gasket, using 850℃×0.5h normalizing and 720℃×3h incomplete annealing, the hardness is basically similar to 125~165HBW, normalizing saves production cycle and high efficiency than incomplete annealing.
SWRM15 steel single-sided rivets are normalized at 840℃×0.5h and recrystallized and annealed at 600℃×4h. The hardness of the former is greater than 95HRB, and the hardness of the latter is 78~88HRB which meets the requirements of riveting performance.
For 45 steel large washers, when the hardness requirement is greater than 200HV, normalizing at 870℃×1h is better than incomplete annealing at 760℃×2.5h. The hardness can reach more than 200HV, and the productivity is significantly higher than annealing.
According to statistics, the cost difference between normalizing and annealing processes is 0.2 yuan/Kg~0.45 yuan/Kg. If the normalizing process is properly selected to replace the annealing process, it can bring considerable benefits to fastener companies while achieving green manufacturing. Economic benefits.
In short, with the development of the fastener industry and the promotion of advanced technology, energy saving and consumption reduction will be in the first place, and the green characteristics of the normalizing process will be more obvious and prominent than the annealing process.

The main purpose and scope of application of electronic tensile testing machine

The main purpose and scope of application of the electronic tensile testing machine: this series of material testing machines are widely used in various small cross-section metal wires, dry mortar, waterproof materials, rubber and plastics, insulation materials, textiles, wires and cables, coatings, non-woven fabrics, and paper Test various physical properties such as stretching, tearing, peeling, elongation, etc. for various materials, as well as mechanical properties of other parts. Comply with GB2611-81 “General Standard for Testing Machines”, “Test Methods for Asphalt Waterproof Rolls” GB/T328-89, “Determination of Tensile Properties of Vulcanized Rubber and Mat Plastic Rubber” GB/T528-1998, “Polyvinyl Chloride Waterproof Rolls” “GB12952-2003, “Petroleum Asphalt Fiberglass Tire Felt” GB/T14686-93 and other national standards.

Utilize the function of spring

Spring measurement function
We know that within the limits of elasticity, the extension (or contraction) of extension springs, compression springs, torsion springs, bending springs, springs, and coil springs is proportional to the external force. Use the nature of the spring to make a spring balance.
Spring compression function
Observing various electrical switches, you will find that one of the two contacts of the switch must be equipped with a spring to ensure that the two contacts are in close contact and are in good conduction. If the contact is poor, the resistance at the contact will increase, and the heat generated when the current passes will increase. In severe cases, the metal at the contact will melt. The two metal posts of the bayonet base are equipped with springs for good contact; as for the central metal piece of the screw base and the plug-in metal pieces of all sockets are reeds, their function is to make the two sides in close contact to maintain Same good. In a magnetic tape, there is a piece of phosphor bronze reed, which uses the elastic force generated when it is bent and deformed to make the magnetic head closely contact the tape. There is a long coil spring in the stapler. On the one hand, it is used to tighten the staples. On the other hand, when the front staple is pushed out, the back staples can be sent to the front to prepare the staples to be pushed out comfortably. In this way, the nails can be pushed to the front automatically one by one until all the nails are pushed out. Many machines feed automatically, and the automatic loading of bullets in automatic rifles relies on this function of springs. In addition, clips like clothes clips, ball-point pens, and pen holders are clamped on clothes by the pressing function of springs.
Spring return function
The spring is deformed under the action of external force, and after the external force is removed, the spring can be restored to its state. Many tools and equipment use springs to reset. For example, many building door hinges are equipped with return springs. After people enter and exit, the door will automatically reset. People also use this function to make automatic umbrellas, automatic pencils and other supplies, which is very convenient. In addition, various buttons and keys are also indispensable for return springs.
Spring drive function
Mechanical clocks and clockwork toys are driven by winding up the clockwork. When the mainspring is tightened, the mainspring is bent and deformed, storing a certain amount of elastic potential energy. After release, the elastic potential energy is transformed into kinetic energy, which is driven to rotate by the transmission device. In toy guns, starting guns and military guns, they also work with springs.
Spring buffer function
A spring is installed between the vehicle frame and the wheel, and the elasticity of the spring is used to slow down the bumps of the vehicle.
Spring vibration sound function
When air flows from the reed hole in the harmonica or accordion, it impacts the reed and the reed vibrates to make a sound.

The name and size relationship of each part of the spring

Spring is an elastic element widely used in the mechanical and electronic industries. The spring can produce greater elastic deformation when loaded, converting mechanical work or kinetic energy into deformation energy, and the deformation of the spring disappears and returns to its original shape after unloading. Deformation energy is converted into mechanical work or kinetic energy.
1. The main functions of the spring are:

① Force measurement, such as spring scales and gauge springs;

②Control movement, such as clutch, brake and valve control spring;

③Vibration reduction and buffering, such as buffers, springs of shock absorbers, etc.;

④ Energy storage or energy transmission, such as springs on clocks, meters and automatic control mechanisms.

2. Type of spring:

There are many types of springs, such as compression springs, extension springs, torsion springs and metal wire forming.

3. The name and size relationship of each part of the spring:

(1) Talk about spring wire diameter d: the diameter of the steel wire used to make the spring.

(2) Spring outer diameter D: the maximum outer diameter of the spring.

(3) Spring inner diameter D1: the minimum outer diameter of the spring.

(4) Spring diameter D2: the average diameter of the spring. Their calculation formula is: D2=(D+D1)÷2=D1+d=D-d

(5) t: Except for the support ring, the axial distance between the corresponding points of two adjacent coils of the spring on the pitch diameter becomes the pitch, which is represented by t.

(6) Effective number of turns n: the number of turns that the spring can maintain the same pitch.

(7) Number of support turns n2: In order to make the spring work evenly, to ensure that the end of the axis is vertical, the two ends of the spring are often tightened during manufacturing. The number of tight turns only serves as a support and is called a support ring. Generally there are 1.5T, 2T, 2.5T, and 2T is commonly used.

(8) Total number of turns n1: the sum of effective number of turns and support ring. That is, n1=n+n2.

(9) Free height H0: the height of the spring without external force. Calculated by the following formula: H0=nt+(n2-0.5)d=nt+1.5d (when n2=2)

(10) Spring unfolding length L: The length of steel wire required to wind the spring. L≈n1(ЛD2)2+n2 (compression spring) L=ЛD2n+ hook extension length (tension spring)

(11) Spiral direction: there are left and right rotations. Right-handed is commonly used, and right-handed is generally used if it is not indicated in the drawing.

4. The prescribed drawing method of the spring:

(1) On the view of parallel coil spring lines, the contour lines of each circle are drawn as straight lines.

(2) If the effective number of turns is more than 4 turns, you can only draw 1 to 2 turns at both ends (not including support ring). The middle is connected by a dotted line through the center of the spring wire.

(3) On the drawing, when the direction of rotation of the spring is not specified, the coil spring is drawn as right-handed, and the left-handed spring is also drawn as right-handed, but the word “left” should be marked.

Titanium alloy cutting performance

Cutting characteristics
When the hardness of titanium alloy is greater than HB350, cutting is particularly difficult, and when the hardness is less than HB300, it is prone to sticking and cutting is difficult. But the hardness of titanium alloy is only one aspect that is difficult to cut. The key lies in the influence of the combination of chemical, physical and mechanical properties of titanium alloy on its machinability. Titanium alloy has the following cutting characteristics:

(1) Small deformation coefficient: This is a significant feature of titanium alloy cutting processing, and the deformation coefficient is less than or close to 1. The sliding friction distance of chips on the rake face is greatly increased, which accelerates tool wear.

(2) High cutting temperature: Because the thermal conductivity of titanium alloy is very small (only equivalent to 1/5 ~ 1/7 of 45 steel), the contact length between the chip and the rake face is extremely short, and the heat generated during cutting is not easy to transfer It is concentrated in a small area near the cutting area and the cutting edge, and the cutting temperature is very high. Under the same cutting conditions, the cutting temperature can be more than twice as high as when cutting 45 steel.

(3) The cutting force per unit area is large: the main cutting force is about 20% smaller than that during steel cutting. Because the contact length between the chip and the rake face is extremely short, the cutting force per unit contact area is greatly increased, which is likely to cause chipping. At the same time, due to the small modulus of elasticity of titanium alloy, it is prone to bending deformation under the action of radial force during processing, causing vibration, increasing tool wear and affecting the accuracy of parts. Therefore, the process system is required to have better rigidity. Supreme enterprise

(4) Chilling phenomenon is serious: due to the high chemical activity of titanium, it is easy to absorb oxygen and nitrogen in the air to form a hard and brittle skin at high cutting temperature; at the same time, plastic deformation during cutting will also cause surface hardening . Chilling phenomenon not only reduces the fatigue strength of parts, but also aggravates tool wear, which is a very important feature when cutting titanium alloys.

(5) The tool is easy to wear: After the blank is processed by stamping, forging, hot rolling and other methods, a hard and brittle uneven skin is formed, which can easily cause chipping, making the removal of the hard skin the most difficult process in titanium alloy processing. In addition, due to the strong chemical affinity of titanium alloy to tool materials, the tool is prone to bond wear under the conditions of high cutting temperature and high cutting force per unit area. When turning titanium alloy, sometimes the wear of the rake face is even more serious than that of the flank; when the feed rate f<0.1 mm/r, the wear mainly occurs on the flank; when f>0.2 mm/r, the front The blade face will be worn; when using carbide tools for fine turning and semi-finishing turning, the wear of the flank face is more suitable for VBmax<0.4 mm.

Tool material

Cutting titanium alloy should start from the two aspects of lowering cutting temperature and reducing adhesion. It is suitable to choose tool materials with good red hardness, high bending strength, good thermal conductivity, and poor affinity with titanium alloys. YG cemented carbide is more suitable. Due to the poor heat resistance of high-speed steel, tools made of cemented carbide should be used as much as possible. Commonly used cemented carbide tool materials include YG8, YG3, YG6X, YG6A, 813, 643, YS2T and YD15.

Coated inserts and YT cemented carbide will have a violent affinity with titanium alloys, which will aggravate the bonding and wear of the tool, and are not suitable for cutting titanium alloys; for complex and multi-edge tools, high-vanadium high-speed steel (such as W12Cr4V4Mo ), high-cobalt high-speed steel (such as W2Mo9Cr4VCo8) or aluminum high-speed steel (such as W6Mo5Cr4V2Al, M10Mo4Cr4V3Al) and other tool materials, suitable for making drills, reamers, end mills, broaches, taps and other tools for cutting titanium alloys.

Using diamond and cubic boron nitride as tools for cutting titanium alloys can achieve significant results. For example, the cutting speed can reach 200 m/min under the condition of emulsion cooling with natural diamond tools; if the cutting fluid is not used, the allowable cutting speed is only 100 m/min at the same amount of wear.

Precautions

In the process of cutting titanium alloy, the matters that should be paid attention to are:

(1) Due to the small modulus of elasticity of titanium alloy, the clamping deformation and force deformation of the workpiece during processing will reduce the processing accuracy of the workpiece; the clamping force should not be too large when the workpiece is installed, and auxiliary support can be added when necessary.

(2) If a cutting fluid containing chlorine is used, it will decompose and release hydrogen at high temperatures during the cutting process, which will be absorbed by titanium and cause hydrogen embrittlement; it may also cause high-temperature stress corrosion cracking of titanium alloys.

(3) The chloride in the cutting fluid may also decompose or volatilize toxic gas during use. Safety protection measures should be taken during use, otherwise it should not be used; after cutting, the parts should be thoroughly cleaned with a chlorine-free cleaning agent in time to remove chlorine residues Things.

(4) It is forbidden to use lead or zinc-based alloy tools and fixtures to contact titanium alloys, and copper, tin, cadmium and their alloys are also prohibited.

(5) All tools, fixtures or other devices in contact with the titanium alloy must be clean; the cleaned titanium alloy parts must be protected from grease or fingerprint contamination, otherwise it may cause salt (sodium chloride) stress corrosion in the future.

(6) Under normal circumstances, there is no risk of ignition when cutting titanium alloys. Only in micro-cutting, the small chips cut off will ignite and burn. In order to avoid fire, in addition to pouring a large amount of cutting fluid, it is also necessary to prevent the accumulation of chips on the machine tool. The tool should be replaced immediately after being blunt, or the cutting speed should be reduced, and the feed rate should be increased to increase the chip thickness. In case of fire, fire extinguishing equipment such as talcum powder, limestone powder, dry sand should be used to extinguish the fire. Carbon tetrachloride and carbon dioxide fire extinguishers are strictly prohibited, and watering is prohibited, because water can accelerate the combustion and even cause hydrogen explosion.

Titanium alloy features:

Titanium has a relatively low density of 4.5g/cm3, which is only 60% of iron. It is usually called light metal with aluminum and magnesium, and its corresponding titanium alloys, aluminum alloys, and magnesium alloys are called light alloys. Many countries in the world have recognized the importance of titanium alloy materials, and have successively conducted research and development on titanium alloy materials, and have been practically applied. Titanium is an important structural metal developed in the 1950s. Titanium alloys are widely used in various fields because of their high specific strength, good corrosion resistance, high heat resistance, and easy welding. High strength and easy welding are beneficial to the manufacture of golf club heads.

The first practical titanium alloy was Ti-6Al (aluminum)-4V (alum) alloy successfully developed by the United States in 1954. Ti-6Al-4V alloy has reached a good level in terms of heat resistance, strength, plasticity, toughness, formability, weldability, corrosion resistance and biocompatibility. The amount of Ti-6Al-4V alloy used has accounted for 75-85% of all titanium alloys. Many other alloys can be regarded as modifications of Ti-6Al-4V alloy. At present, there are hundreds of titanium alloys developed in the world, and there are 20 to 30 kinds of the most famous alloys, for example, Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-2Al-2.5Zr, Ti -32Mo, Ti-Mo-Ni, Ti-Pd, Ti-811, Ti-6242, Ti-1023, Ti-10-5-3, Ti-1100, BT9, BT20, IMI829, IMI834, etc.; for ball The rods are 10-2-3, SP700, 15-3-3-3 (commonly referred to as β titanium), 22-4, DAT51.