Renoho Precision Machinery Technology Co.,Ltd: Taking a Plunge: Taking a Plunge Although standard microdrills aren’t generally available below 0.002", microendmills that can be used to “plunge” ...
Taking a Plunge
Although standard microdrills aren’t generally available below 0.002", microendmills that can be used to “plunge” a hole are. “When people want to drill smaller than that, they use our endmills and are pretty successful,” Burton said. However, the holes can’t be very deep because the tools don’t have long aspect, or depth-to-diameter, ratios. cnc milling machineTherefore, a 0.001"-dia. endmill might be able to only make a hole up to 0.020" deep whereas a drill of the same size can go deeper because it’s designed to place the load on its tip when drilling. This transfers the pressure into the shank, which absorbs it.
Performance offers endmills as small as 5 microns (0.0002") but isn’t keen on increasing that line’s sales. cnc milling machine “When people try to buy them, I very seriously try to talk them out of it because we don’t like making them,” Burton said. Part of the problem with tools that small is the carbide grains not only need to be submicron in size but the size also needs to be consistent, in part because such a tool is comprised of fewer grains. “The 5-micron endmill probably has 10 grains holding the core together,” Burton noted.
He added that he has seen carbide powder containing 0.2-micron grains, which is about half the size of what’s commercially available,cnc milling machine but it also contained grains measuring 0.5 and 0.6 microns. “It just doesn’t help to have small grains if they’re not uniform.”
To further aid chip evacuation, Davis recommends applying an oil-based metalworking fluid instead of a waterbased coolant because oil provides greater lubricity. But if a shop prefers using coolant, Cnc machining the fluid should include EP (extreme pressure) additives to increase lubricity and minimize foaming. “If you’ve got a lot of foam,” Davis noted, “the chips aren’t being pulled out the way they are supposed to be.”
He added that another way to enhance a tool’s slipperiness while extending its life is with a coating, such as titanium aluminum nitride. TiAlN has a high hardness and is an effective coating for reducing heat’s impact when drilling difficult-to-machine materials, like stainless steel.
David Burton, general manager of Performance Micro Tool, Janesville, Wis., disagrees with the idea of coating microtools on the smaller end of the spectrum. “Coatings on tools below 0.020" typically have a negative effect on every machining aspect, from the quality of the initial cut to tool life,” he said. That’s because coatings are not thin enough and negatively alter the rake and relief angles when applied to tiny tools.
However, work continues on the development of thinner coatings, and Burton indicated that Performance Micro Tool, Cnc machiningwhich produces microendmills and microrouters and resells microdrills, is working on a project with others to create a submicron-thickness coating. “We’re probably 6 months to 1 year from testing it in the market,” Burton said. The microdrills Performance offers are basically circuit-board drills, which are also effective for cutting metal. All the tools are without through-coolant capability. “I had a customer drill a 0.004"-dia. hole in stainless steel, and he was amazed he could do it with a circuit-board drill,” Burton noted, adding that pecking and running at a high spindle speed increase the drill’s effectiveness.
The requirements for how fast microtools should rotate depend on the type of CNC machines a shop uses and the tool diameter, with higher speeds needed as the diameter decreases. (Note: The equation for cutting speed is sfm = tool diameter × 0.26 × spindlespeed.) Although relatively low, 5,000 rpm has been used successfully by Burton’s customers. “We recommend that our customers find the highest rpm at the lowest possible vibration—the sweet spot,” he said.
In addition to minimizing vibration, a constant and adequate chip load is required to penetrate the workpiece while exerting low cutting forces and to allow the rake to remove the appropriate amount of material. If the drill takes too light of a chip load, the rake face wears quickly, becoming negative, and tool life suffers. This approach is often tempting when drilling with delicate tools.
“If the customer decides he wants to baby the tool, he takes a lighter chip load,” Burton said, “and, typically, the cutting edge wears much quicker and creates a radius where the land of that radius is wider than the chip being cut. He ends up using it as a grinding tool, trying to bump material away.” For tools larger than 0.001", Burton considers a chip load under 0.0001" to be “babying.” If the drill doesn’t snap, premature wear can result in abysmal tool life.
He added: “You would think with 0.0003" runout and a chip load a third that, say, 0.0001" to 0.00015", the tool would break immediately because one flute would be taking the entire load and then the back end of the flute would be rubbing.
When drilling, he indicated that up to 0.0003" TIR should be acceptable because once the drill is inside the hole, the cutting edges on the end of the drill continue cutting while the noncutting lands on the OD guide the tool in the same direction. Minimizing run out becomes more critical as the depth-to-diameter ratio increases. This is because the flutes are not able to absorb as much deflection as they become more engaged in the workpiece. Cnc machiningUltimately, too much runout causes the tool shank to orbit around the tool’s center while the tool tip is held steady, creating a stress point where the tool will eventually break.
Options for micro-holemaking
As in the macroscale-machining world, holemaking is one of the most— if not the most—frequently performed operations for micromachining. Cnc machining Many options exist for how those holes are created. Each has its advantages and limitations, depending on the required hole diameter and depth, workpiece material and equipment requirements. This article covers holemaking with through-coolant drills and those without coolant holes, plunge milling, microdrilling using sinker EDMs and laser drilling.
Getting coolant to the drill tip while the tool is cutting helps reduce the amount of heat at the tool/workpiece interface and evacuate chips regardless of hole diameter. Cnc machining But through-coolant capability is especially helpful when deep-hole microdrilling because the tools are delicate and prone to failure when experiencing recutting of chips, chip packing and too much exposure to carbide’s worst enemy—heat.
When applying flood coolant, the drill itself blocks access to the cutting action. “Somewhere about 3 to 5 diameters deep, the coolant has trouble getting down to the tip,” said Jeff Davis, vice president of engineering for Harvey Tool Co., Rowley, Mass. “It becomes wise to use a coolant-fed drill at that point.”
In addition, flood coolant can cause more harm than good when microholemaking. “The pressure from the flood coolant can sometimes snap fragile drills as they enter the part,” Davis said.
The toolmaker offers a line of through-coolant drills with diameters from 0.039" to 0.125" that are able to produce holes up to 12 diameters deep, as well as microdrills without coolant holes from 0.002" to 0.020".
Having through-coolant capacity isn’t enough, though. Coolant needs to flow at a rate that enables it to clear the chips out of the hole. Davis recommends, at a minimum, 600 to 800 psi of coolant pressure. “It works much better if you have higher pressure than that,” he added.
To prevent those tiny coolant holes from becoming clogged with debris, Davis also recommends a 5μm or finer coolant filter.
Another recommendation is to machine a pilot, or guide, hole to prevent the tool from wandering on top of the workpiece and aid in producing a straight hole. When applying a pilot drill, it’s important to select one with an included angle on its point that’s equal to or larger than the included angle on the through-coolant drill that follows. The pilot drill’s diameter should also be slightly larger.Cnc machining For example, if the pilot drill has a 120° included angle and a smaller diameter than a through-coolant drill with a 140° included angle, “then you’re catching the coolant-fed drill’s corners and knocking those corners off,” Davis said, which damages the drill.
Although not mandatory, pecking is a good practice when microdrilling deep holes. Davis suggests a pecking cycle that is 30 to 50 percent of the diameter per peck depth, depending on the workpiece material. This clears the chips, preventing them from packing in the flute valleys.
Cylinder processing the choice of cutting parameters
Engine block choice of cutting parameters including cutting speed, feed rate and feed rate option. Cnc milling machine As the processing equipment is used in high precision and rigidity of machine tools and high-speed machining centers in order to ensure the efficiency of cutting may be the appropriate choice of cutting a larger amount.
The main processing engine block surface plane and bearing bore, cylinder bore holes such as the processing, while the plane and bearing bore, cylinder bore of the processing method is mainly milling and boring, Cnc milling machine so the discussion here, the choice of cutting parameters are mainly milling and Boring choice of cutting parameters.
(1) milling the choice of the amount of usage the choice of milling milling effect is directly related to good or bad. Generally speaking, the choice of dosage milling principles: Face milling cutter should be as much as possible when you first take a larger milling depth and width of milling, and then select the larger milling rate of as much as possible. Milling in a specific amount of choice when many factors involved, but in general, rough milling large margin when the workpiece, processing requirements low, the main consideration of the durability of cutter; Fine Milling margin is small, high precision machining, improvement in the quality processing of primary consideration; In the engine block of the milling process, the use of machine tools as having a high stiffness, high-speed machine tools, big power, rigidity is good, so has chosen the relatively large amount of cutting
(2) boring dosage amount of choice options under the rough finishing process varies. Rough, the selection of a larger depth of cut, finish, the selection of a smaller depth of cut. Depth of cut determined later, as cutting a large amount of use. In the cutting depth and feed rate after the selection ?=can be a reasonable tool to ensure durability under the conditions of use calculations or look-up table method to determine the cutting speed. In general, the rough, choose a lower cutting speed, finishing, the selection of a higher cutting speed. In the engine block boring process, the selection of machine tools as having a high stiffness, high-speed machine tools, big power, good rigidity; tool for foreign advanced tools, high quality, rigidity is good, so has chosen the relatively large amount of cutting.
Through the engine block of the structure and process characteristics of the analysis, discusses the engine block machining process design principles and basis of the choice of cutting parameters, and U-turn at high speed milling and boring, for example, design, Cnc milling machine analysis of the engine cylinder body of high-speed milling and turnover boring process, and in the processing need to pay attention to.
Cylinder surface of the main processing and secondary processes
Cylinder surface and support the main processing operations are:
(1) plane processing At present, the milling of engine blocks is the primary means of planar processing, Cnc machining domestic milling feed rate is generally 300-400mm/min, and foreign 2000-4000mm/min milling feed rate compared to far cry, to be on increasing, therefore, improve the milling feed rate, reduce overhead time is to improve the productivity of the major means of finishing a number of plane engine block when the milling feed rate to reach 2399 mm / min, greatly improved efficiency; Top surface of the cylinder milling is a key process in the process, the flatness requirements for 0.02/145mm, the surface roughness of Ra1.6um. Processing in the cylinder, the use of side and spindle bearing bore positioning, top, bottom and middle vagay only aperture while processing used in the processing line outside of the knife device can better meet the engine block machining accuracy
(2) General holes machining holes in general are still using the traditional processing of drilling, expansion, boring, reaming, tapping and other craft approach. Issues in the design process of specific programs, use of coated cutting tools, Cnc machining cutting tools and other advanced tools within the cooling, and using a large flow of cooling systems, greatly improving the cutting speed, improved productivity; he key process before ining ProceW
(3) deep hole processing of the traditional processing method is used to grade twist drill feed, low efficiency of their production, processing and quality is poor. The deep hole in the engine block processing, the use of gun drilling process;
(4) The three-axis machining holes for the cylinder-axis machining holes holes of high precision, long working hours of the restrictive process. Thus, work arrangements, processing methods, tools and so on should be special attention. All cover pre-processing, that is, semi-circular hole and the cylinder block main bearing cap of the shortage of processing, its main purpose is to remove blank margin, release stress, to prepare for the post-order processing; in crankshaft machining processing center hole, using double-sided Boring, boring the first holes in the crankshaft hole at one end to 1 / 2 length, and then turn 180 degrees workbench, from the other end and then bore another 1 / 2 length.
(5) The cylinder bore machining cylinder hole cylinder machining processing is a key process in the one, under normal circumstances, the machining process as a rough boring, semi-fine boring, precision boring and honing. Cylinder bore wall for the early detection of casting defects, eliminate stress, should be thick cylinder boring holes in advance; due to the structural characteristics of the different cylinder bore, must be in honing process to improve the cylinder bore surface quality. In the high-volume production, the cylinder bore honing generally use the multi-axis grinding machine or honing Automatic Line. Here we use honing automatic lines, from the coarse-heng. Fine-heng and testing equipment, composed of three;
(6) Cleaning Cleaning is divided into wet cleaning and dry cleaning. Machining cylinder automatic production line using a large flow of wet cleaning;
(7) Detect points outside the line detection and line detection of two kinds. Quality inspection in the engine block, Cnc machining according to the actual vity; he key process before iniXsituation with lines outside the detection, the main use of coordinate measuring machine integrated measurements of the cylinder, each 200 samples 1-5 pieces, each class random one.
Machining Processing Stages and processes of the arrangements
Often a part of many apparent need for processing, of course, the surface machining accuracy are different. Processing of high precision surface, often after repeated processing;Cnc machining As for the processing of the surface of low precision, only need to go through one or two on the list. Thus, when the development process in order to seize the “processing high precision surface,”this conflict, the reasonable arrangement processes and rational division stage of processing. Arrange the order of the principle of process is: after the first coarse refined, the first surface after the hole, the first benchmark other. In the engine block machining, the same should follow this principle
(1) roughing stage engine block machining process, the arrangements for roughing process, to fully carry out rough rough, trim most of the margin in order to ensure production efficiency;
(2) semi-finishing phase of the engine block machining, in order to ensure the accuracy of some important surface processing, and arrange some semi-finishing operations, will be required accuracy and surface roughness of the surface of the middle of some processing to complete, while demanding the surface of semi-finished, to prepare for future finishing;
(3) The finishing stage of requiring high accuracy and surface roughness of the surface processing;
(4) secondary processing, such as small surface screw holes, you can finish of the major surface after the one hand, when the workpiece deformation process little impact at the same time also reduced the rejection rate; In addition, if the main surface of a waste, Cnc machining these small the surface will not have to be processed, thus avoiding a waste of man-hours. However, if the processing is very easy for a small surface bumps the main surface, it should be placed on a small surface finish prior to the main surface finishing;
(5) should make proper arrangements for secondary processes such as product inspection process, in part roughing stage, the key process before ining Processing Stages and processTand after processing, spare parts all the processing has been completed, should be appropriate arrangements.
Stage of processing division, has the following advantage Cnc machining to ensure accuracy; second, finishing on the back, and will not damage during transport the surface of the workpiece has been processed; again, first roughing the surface defects can be detected early and promptly deal with rough, do not waste working hours. But most small parts, do not sub very thin.
Process design basis
Affect the engine block part of the process design factors are manifold. Specifically, can be understood from the following aspects.
(1) product object, product drawings and precision parts technical documents related to the complexity of the engine block under the precision requirements of the process to take corresponding measures. Production targets for the four-cylinder automobile engine cylinder block;
(2) the production program, the production of the nature and type of production of the engine block the production program of 400 million;
(3) The annual effective system of work equipment, working for 320 days, with an average equipment loading rate of 80%, two shifts, 16 hours / day.
Engine block complex structure, high precision, large size, is thin-walled parts, there are a number of high precision plane and holes.
Engine block machining process characteristics: mainly flat and the hole processing,precision parts processing of flat generally use planing, milling methods such as processing, processing of hole used mainly boring, processing and multi-purpose drilling holes. As the cylinder complex structure, so how to ensure that the mutual position of the surface processing precision is an important issue
The selection of blank
Engine block on the materials used are generally gray cast iron HT150, HT200, HT250, there is also cast aluminum or steel plate, this engine block using high-strength alloy cast iron. precision parts Cylinder in the processing prior to aging treatment in order to eliminate stress and improve the rough casting mechanical properties.
Improve the rough accuracy, reduction of machining allowance, is to improve the automated production line system productivity and processing quality of the important measures. As the foreign box-type parts of rough quality and high precision, and its production-line system has been implemented directly on the blank line, not only eliminating the need for blank check device also saves the rough quality problems due to waste of machining time, increase overall efficiency. Therefore, the refinement of rough is to improve the productivity of the most promising way out. For the engine block production line, can be rough in parts on-line pre-milling six face, removing most of the margin, to facilitate direct on-line parts.
Process design principles
Design Technology program should be to ensure product quality at the same time, give full consideration to the production cycle,Cnc machining cost and environmental protection; based on the enterprises ability to actively adopt advanced process technology and equipment, and constantly enhance their level of technology Engine block machining process design should follow the following basic principles:
(1) The selection of processing equipment, processing equipment, the principle of selection adopted the principle of combining rigid-flexible, processing each horizontal machining center is located mainly small operations with vertical machining center, the key process a crank hole, cylinder hole, balancer shaft hole High-speed processing of high-precision horizontal machining center, Cnc machining an upper and lower non-critical processes before and after the four-dimensional high-efficiency rough milling and have a certain adjustment range of special machine processing;
(2) focus on a key process in principle process the body cylinder bore, crankshaft hole, Balance Shaft hole surface finishing and the combination of precision milling cylinder head, using a process focused on a setup program to complete all processing elements in order to ensure product accuracy The key quality processes to meet the cylinder capacity and the relevant technical requirements;
(3) All fixtures are used hydraulic clamp, clamping components, hydraulic pumps and hydraulic control components used in Germany or the United States producing high quality and reliable components;
(4) The whole line used in all wet processing, using standalone BTA, high-precision machining processes critical horizontal machining center with constant cooling and to install high-precision high-voltage double-circuit band-pass fine filtration system, all with high-pressure processing center in the cold. According to the technological characteristics of automobile engine cylinder block and the production mandate, the engine block machining automatic production line is composed of horizontal machining center CWK500 and CWK500D machining centers, special milling / boring machine, vertical machining centers matec-30L and other appliances.
(1) top and bottom, and tile covered only the combination of aperture rough milling machine dedicated to this machine to double-sided horizontal milling machine, using moving table driven parts, machine tools imported Siemens S7-200PLC system control, control cabinet set up an independent, cutting automate the process is completed and two kinds of automatic and adjust the state;
(2) high-speed horizontal machining center machining center can be realized CWK500 the maximum flow of wet processing, but because of equipment, automatic BTA treatment system through the built-in tray under the wide-type chip conveyor and the completion of the machining center can be dry processing; machine tool spindle speed 6000r/min, rapid feeding speed 38m/min;
(3)The combination of front and rear face rough milling machine tool using hydraulic transmission; control system imported Siemens S7-200PLC system control, machine tools have a certain flexibility;
(4) The special machine TXK1500 this machine vertical machining center by the modification of shape, Cnc machining with vertical machining center features and performance, this machine has high strength, high wear-resistant, high stability, high accuracy, high-profile etc.;
(5) high-speed vertical machining center matec-30L of the machining center spindle high speed 9000r/min. Control system uses Siemens SINUMERIK840D control system;
(6) high-speed horizontal machining center spindle CWK500D highest speed 15000r/min
Engine parts in the engine block is a more complex structure of spare parts box, Cnc machining its high precision, processing, complex process, and the processing quality will affect the overall performance engine, so it has become the engine manufacturer's focus parts one.
Engine block is the basic engine parts and skeleton, when the general assembly of the base components.Cylinder's role is supporting and ensuring the piston, connecting rod, Cnc machining crankshaft and other moving parts work, the exact location; to ensure the engine ventilation, cooling and lubrication; to provide a variety of auxiliary systems, components and engine installation.
Cylinder cast for a whole structure, and its upper part 4 cylinder mounting hole; cylinder standard cylinder is divided into upper and lower divisions into two parts; cylinder to the rear of the front-side arrangement of the previous three coaxial mounting hole of the camshaft and the idler axle hole.
Cylinder process features are: the structure of complex shape; processing plane, more than holes; uneven wall thickness and stiffness is low; processing of high precision typical of box-type processing part.
The main processing of the surface of cylinder block top surface, the main bearing side, cylinder bore, the main and camshaft bearing bore holes and so on, they will directly affect the machining ccuracy of the engine assembly precision and performance, mainly rely on precision equipment, industrial fixtures reliability and processing technology to ensure the reasonableness.
Technology program is the preparation of the master process is to process planning and key process equipment design guidance documents. Cnc machining The correct process of program design, facilitate the systematic application of new scientific and technological achievements and advanced production experience, to ensure product quality, improve working conditions, and improve process technology and process management level.