Drilling of difficult to machine materials-1

Drilling high-precision holes in difficult to machine materials can be challenging. In order to successfully complete the difficult processing of materials from the large-scale titanium alloy or composite parts of the aviation industry, to the small size of the Inconel alloy medical device the drilling process, need to overcome, including cutting heat, high abrasion, high hardness, High viscosity of the various difficulties. In order to cope with these problems, it is necessary to optimize the drill bits in terms of geometrical shape, cutting edge preparation, base grade, tool coating and coolant transportation.

Forming chips that are easy to handle

“The end user always wants to get higher drilling rates, longer tool life and better hole quality,” said the R & D staff. “At our annual technical training seminars for users and resellers, we first Will tell them that in any efficient drilling, the first must be formed enough small chips, so that it can be smoothly discharged from the hole. Drill must have a reasonable cutting edge shape, and once the formation of the appropriate chip, must also be cut The liquid medium provides sufficient kinetic energy to allow the chip flow to be discharged from the hole. In order to achieve smooth chip removal, the coolant system consisting of the internal cooling tool and the high pressure coolant is indispensable because the appropriate coolant system can convert more heat from Take the tool away.

The geometrical shape, cutting edge strength, material grade and coating of the drillable high-efficiency drill bits are specially developed for drilling of stainless steel, superalloy and nickel-based alloys. Austenitic stainless steel for food machinery and pressure vessel industry is difficult to process. These materials have a large deformation rate, and in drilling austenitic stainless steel, the large deformation rate will be converted into a very thick chip. In this case, the drill bit must have the correct geometry and the cutting edge should be prepared with a suitable coating to ensure that the drill bit is not easily broken and can withstand high cutting temperatures.

Composite materials, metal matrix composites, phenolic resin materials and carbon fiber composites have a very small tensile strength and great abrasiveness, drilling these materials, like sandpaper wrapped with drill bit hard friction, Easy to wear.

Main points of stainless steel tapping -2

Workpiece clamping is likely to be another factor problem. Tapping on the stainless steel parts, should ensure that the workpiece clamping rigid loading, prevent the workpiece vibration. The key factors of the screw size and quality also affect the processing. Standard thread 2B path height is 65% 83.3%. maximum height (100%) thread is a perfect triangle thread. 65%, the amount of material removed to less than 83.3% of the thread, and the amount of material removed tap is less, the torque required is smaller, the tap life is longer.

The workpiece material cold hardening will shorten the life of tap. In order to minimize cold hardening, should adopt the appropriate drill, and the feed rate and cutting speed appropriate to the drilling hole.

Tap the geometry and the coating is also very important. Tapping the blind hole, should use large spiral slot taps with positive rake angle of the cutting edge, to increase the shear angle, improve chip performance. Processing high hardness stainless steel, it needs to use usually can significantly improve the performance of tapping with high strength cutting edge and a small spiral angle tap.TiN or TiCN coating.

There is no problem of tapping chip extrusion, but requires tapping torque, more so, the use of cooling liquid effectively. Extrusion tapping, cutting cone tooth number should be less than the standard cone bottom. Use the plunger type tap may make the workpiece material serious cold hardening.

Thread milling is an alternative processing workshop can be considered. This process can control the cutting speed and feed rate, and can prevent thread tearing. However, the processing speed of thread milling than tapping slowly, may cause the production bottleneck. In addition, but also by the thread cutter length to diameter ratio limit, screw depth should not normally be more than 2 times the diameter.

Stainless steel tapping quality requirements continue to improve, not only the use of suitable taps, but also need to choose the right processing parameters.

Main points of stainless steel tapping -1

Tapping is a difficult process. Because the tapping feed rate is a function of tap pitch, so as to be artificially controlled. For example, the specifications for the 1/2-20 tap its feed rate is only 0.050ipr (1.27mm/r). Therefore, the processing is very difficult to control the chip load per tooth tapping is usually the final processing. Process parts, if the tap break in the workpiece hole, it may cause great economic losses.

Stainless steel tapping is a unique challenge. Stainless steel is difficult to machine materials, will produce long is not easy to break chips. In addition, stainless steel is prone to cold hardening stainless steel tapping. In order to improve the productivity and prolong tool life, must consider the machinability of the stainless steel, the cutting performance of tapping process and tap itself.

The machinability of the stainless steel and carbon steel or alloy steel are more difficult to be quite different, most stainless steel cutting.400 series of ferritic stainless steel although also can produce slender chips, but the process is relatively easy. While the 300 series austenitic stainless steel has great tendency of viscous and rapid cold hardening, the processing difficulty is great. Double phase stainless steel is a mixture of ferrite stainless steel and austenitic stainless steel, with good toughness and strength, but also prone to cold hardening.

The problem of stainless steel tapping is usually characterized by rough and broken threads, which kill the tap and cause it to break. The flaw in the tap itself may be the root cause. However, there are usually some other reasons

The need to use stainless steel tapping with high lubricity cooling liquid. Tapping is usually one of the processing methods of cutting load maximum, if insufficient lubrication of the cooling liquid and its adverse effects will be faster than most other processing to emerge.

How to composite machining -3

In general, cutting sharp corner is one of the key elements to reduce the cutting heat. Cutter milling and drilling of composite materials is often used before Taisho angle, in order to minimize the amount of heat, to achieve rapid, sharp, neat cutting. These tools also have a greater angle, to prevent the cutting edge friction heating go and the workpiece in the knife.

1.the clamping of the workpiece

Although the processing of composite parts needed may be relatively simple — often only need drilling and trimming, but a fixture for supporting these parts itself may have very high requirements of the design. In fact, the fixture parts processing for composite materials may require costly investment projects. In order to achieve clean cutting. To ensure that the workpiece does not wear pilling, not delaminate, requires reliable positioning of the workpiece, firm clamping, will not vibrate. The machining of composite materials (especially machining thin-walled) usually requires the use of vacuum adsorption clamp and the shape of workpiece precision fit. Select the processing workshop of mechanical clamping device is usually used damping pad.

2.machining machine tools

The contour shape of composite aircraft parts generally require the processing of five axis machine tools. Some previous machining metal parts workshop may use their original five axis machine tool. However, processing of the composite material (at least CFRP processing), usually does not require processing metal materials as big machine power and torque. In fact, in some parts of the metal processing usually cannot light CNC router, can effectively CFRP processing and other composite materials.

How to composite machining -2

To some extent, processing of the composite material is actually the process reversed, because the workshop’s attention to different parts of the process. The metal material processing aviation parts need a power machine, but only need to use common tools, and can ensure the safety of the fixture simple processing. On the contrary, milling and drilling of composite materials is usually carried out in the light machine power is much smaller, but may need to adopt high-end tool, fixture and to use custom, so that in the whole process of the work piece to prevent its close support, rigid thin wall vibration and damage.

Here are some key points of processing of carbon fiber composite materials may need to be considered.

1.tool materials

Hard alloy cutter can be used for processing composite materials, but because of the short life, in the process often requires frequent tool changing.

Diamond cutting tool may have longer service life. The process of CFRP, diamond tools available include diamond abrasive grinding rod, CVD diamond coating tools or integral PCD blade.

An unusual tool developed specifically for the processing of composite materials is “the whole sintering diamond tool, the tool is the diamond material filling slot in hard alloy handle specially designed and manufactured in direct sintering.

2.tool geometry

At least in one aspect, the composite “crush” removal mechanism of metal materials with “deformation” removal mechanism is similar as in metal cutting, the cutting energy is converted to heat.

CFRP heat is especially difficult because the processing will be generated when the chip can take away the heat, and the thermal conductivity of composite materials is poor. The resulting heat accumulation of the matrix material in danger of melting or otherwise damaged. The coolant may also It doesn’t help the situation. composite materials because the processing, some parts are not allowed to use the cooling liquid therefore, only through reasonable selection of tool and tool path to suppress the cutting heat.

How to cut composite materials?-1

Machining mechanism of composites

Cutting composite materials may look similar to cutting metal materials, but in practice, the two mechanisms are very different.

Composite parts can be put in the metal cutting machine processing, and also can use tool similar to cutting metal parts. However, once the cutting edge cut composite workpiece, and reveals the essential difference between the two – metal cutting the material removal mechanism is completely different.

Metal cutting is the material removal mechanism of plastic deformation. The workpiece material cutting tool material than soft, in the cutting edge formed on the chip flow. In the machining of composite materials, and produce chips in the true sense not. Instead, with the “crush” to describe the material removal mechanism may be more appropriate. The workpiece material is not shear removal, the cutting edge is chopped carbon fiber hard. In this process, the cutting edge to withstand the severe abrasion, which may lead to the rapid wear.

In metal cutting, cutting tool geometry determines the cutting performance of tool material determines its service life. The machining of composite materials are the same. However, in the process of composite material, tool material will become a decision of the cutting performance factors. The composite material may cause rapid wear of tool, so that the tool geometry also change quickly — unless the cutting edge material can resist the abrasion of composite materials, sufficient to maintain its shape and sharpness. Drilling of composite materials, a common phenomenon is that the first two holes may be machined with good quality of drilled hole, but soon there will be stratified in third hole, crack or other defects that just because the orifice, the tool wear due to its geometry cannot keep cutting clean and tidy.

Selection of drills

1.precision

The tungsten steel drill, first of all need to consider the size precision machining drilling requirements. In general, the processed aperture is smaller, its tolerance is smaller. Therefore, the drill is usually according to the hole size on the classification of the nominal diameter of the bit.

2.stability

In addition to considering the drilling accuracy requirements, select the bits needed to consider the stability of the machine. The machine stability for the safe use of life and the accuracy of drilling bit is very important, therefore need to carefully check the machine tool spindle, fixture and accessories working condition.

3.chip removaland coolant

Chip is the drilling processing problems can not be ignored. In fact, drilling is poor chip removal most of the problems in processing (especially the processing of low carbon steel workpiece), and no matter what bits are unable to avoid this problem. Processing workshop often used externally injected coolant auxiliary chip, but this method is only in the processing and reduce the cutting parameters is less than Kong Shen aperture case.

4.machining cost per hole

Productivity or per hole processing cost is the most important factors influencing the drilling process. In order to improve the productivity, drill manufacturers are dedicated to the study of processing method for integrating multiple operations, and can be used to develop high feed, high speed machining of the drilling tool.

Recovery and reuse of cutting tools

Recovery of cutting tool reuse with a variety of immediate and long-term benefits. Eliminate waste refers to reduce the consumption of resources, help enterprises to reduce costs. Recycling can increase the material supply. In addition, with the use of new raw materials (either by mining, or other means of production) manufacturing tool, process usually required less energy recovery and remanufacturing tool, and pollution to the environment is small. This further reduces the cost and reduces the influence of manufacturing process on the environment.

Before sufficient reason for reuse in the proposed tool recovery, first look at the raw material tool. Because the hardness and toughness of the perfect combination, made of hard alloy blades and other tools for hard 75%. of the global market for the first time in 20s of last century developed the tungsten carbide and cobalt tungsten is a kind of form. Mineral through chemical and heat treatment, the natural ore becomes available form. China segment tungsten production and consumption accounted for 79% of the world and 33%. in the world, 58% are used for the production of tungsten carbide. About 80% of the global production of cobalt from nickel or copper by-product. Application its range is more extensive, although only 12% of the world’s cobalt for the production of wear-resistant alloy (including hard alloy), but for the production of Cutting Tool Co in quantity is still large. Historically, the price of tungsten has maintained relatively Stable, but changes in the past 6 years, from 2004 to 2008, tungsten price doubled two times, rose to about $18 per pound price of tungsten.2008 in August for $13 per pound in December dropped to $11 per pound (Figure 1). The price fluctuation cycle longer cobalt, ranging from $7 A pound to $40 per pound in recent years.2008 August cobalt price is about $18 per pound.

Reamers — Usage, Application notices

1.Usage

Reamer has one or more cutter, rotary cutter to cut holes machined surface of thin metal layers. After processing after the hole cutter can obtain the exact size and shape.

Reamer for reaming workpieces have been drilling (or hole) after machining holes, mainly in order to improve the machining precision of hole, reducing the surface roughness, tool is used for finishing and semi finishing machining of holes, generally small machining allowance.

The reamer used for processing cylindrical hole. More commonly used for processing of the tapered hole reamer is taper reamer, relatively less. According to the use of a hand reamer reamer and machine, machine reamers can be divided into straight shank reamer and taper shank reamer. The hand is a straight handle type.

2.Application notices

A.manual reaming general precautions:

a. the work should be clamped correctly

b.In the reaming process, both hands should be balanced with force

c. When thereamer exits, it can not be reversed. Because the reamer has a rear angle, the reverse of the reamer will cause the chip to plug between the reamer tooth and the hole wall, and it will scratch the hole wall. At the same time, the reamer is easy to wear

d. After the reamer is used, clean it, apply the oil, and pack the box so as not to bruise the blade

B. machine hinges, pay attention to the reaming speed and the amount of the cutter

C.In reaming, a reasonable cooling lubricant must be adopted

D. hand guide conehand is smaller, the front angle and back angle are smaller, and the blade is sharper. Generally, the blade band is narrower, or the guide cone is not at all

 

Reamers-concepts, types

Concepts of reamers:

A reamer is a rotary tool with one or more cutter teeth for removing thin metal on the surface of the machined hole. The reamer has a rotary cutting tool with a straight edge or a spiral edge. It is used for reaming or repairing holes.

Because of the small amount of cutting, the machining accuracy of the reamer is usually higher than that of the drill bit. It can be operated manually or installed on a drilling machine.

Reamer has one or more teeth, with a rotating tool to remove machined holes on the surface of a thin layer of metal. Rotary precision machining tool with straight blade or spiral blade, used for reaming or repair hole, because less cutting its machining precision is usually higher than the bit can be manually operated or installed in the drilling work.

Types of reamers:

The structure of the reamer is mostly composed of the working part and the handle part. The working part mainly takes the function of cutting and calibrating. The diameter of the calibrating part has an inverted taper, and the handle is used for clamping by the clamp, and has the straight handle and the taper handle.

According to different purposes can be divided into many kinds of reamer and so on reamer is more standard, some of our standards are commonly used with GB/T1131 hand reamer, reamer with straight shank machine GB/T1132, GB/T1139 straight shank taper reamer and so on.

To use is divided into reamer reamer and hand reamer reaming machine, according to the shape is divided into cylindrical and conical reamer reamer (1:50 taper pin reamers with Morse taper reamer two types standard taper reamer reamer). The groove direction, a straight groove and the spiral groove, the material used for high speed steel, carbide inserts.

The hand reamer is made of alloy tool steel (9SiCr), the machine reamer is made of high speed steel (HSS), and the machine reamer is divided into straight shank, machine reamer and taper shank machine reamer. The accuracy of the reamer is D4, H7, H8, H9 and so on.