机械类毕业设计外文翻译微孔的加工方法Word文件下载.docx

1、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 a

2、t 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

3、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 isnt 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

4、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 5m or finer coolant filter. Another recommendation is to machine a pilot, or guide, hole to prevent the tool from w

5、andering on top of the workpiece and aid in producing a straight hole. When applying a pilot drill, its important to select one with an included angle on its point thats equal to or larger than the included angle on the through-coolant drill that follows. The pilot drills diameter should also be sli

6、ghtly larger. 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 youre catching the coolant-fed drills corners and knocking those corners off,” Davis said, which damages the drill. Although not mandatory, peck

7、ing 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.Lubricious ChillTo further aid chip evacuation,

8、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, the fluid should include EP （extreme pressure） additives to increase lubricity and minimize foaming. “If youve got a lot of foam,” Da

9、vis noted, “the chips arent being pulled out the way they are supposed to be.” He added that another way to enhance a tools 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 heats impact when

10、 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 machin

11、ing aspect, from the quality of the initial cut to tool life,” he said. Thats 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 T

12、ool, which produces microendmills and microrouters and resells microdrills, is working on a project with others to create a submicron-thickness coating. “Were probably 6 months to 1 year from testing it in the market,” Burton said. The microdrills Performance offers are basically circuit-board drill

13、s, 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 incre

14、ase the drills 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 spindle speed.） Although r

15、elatively low, 5,000 rpm has been used successfully by Burtons customers. “We recommend that our customers find the highest rpm at the lowest possible vibrationthe sweet spot,” he said. In addition to minimizing vibration, a constant and adequate chip load is required to penetrate the workpiece whil

16、e 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 de

17、cides 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 larg

18、er than 0.001, Burton considers a chip load under 0.0001 to be “babying.” If the drill doesnt snap, premature wear can result in abysmal tool life. Too much runout can also be destructive, but how much is debatable. Burton pointed out that Performance purposely designed a machine to have 0.0003 TIR

19、to conduct in-house, worst-case milling scenarios, adding that the company is still able to mill a 0.004-wide slot “day in and day out.” 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 tak

20、ing 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

21、 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. Ultimately, too much runout causes the tool shank to orbit around the tools cente

22、r while the tool tip is held steady, creating a stress point where the tool will eventually break. Taking a Plunge Although standard microdrills arent 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 en

23、dmills and are pretty successful,” Burton said. However, the holes cant be very deep because the tools dont have long aspect, or depth-to-diameter, ratios. Therefore, 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 its de

24、signed 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 isnt keen on increasing that lines sales. “When people try to buy them, I very seriously try to talk them out of it because

25、we dont 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 c

26、ore together,” Burton noted. He added that he has seen carbide powder containing 0.2-micron grains, which is about half the size of whats commercially available, but it also contained grains measuring 0.5 and 0.6 microns. “It just doesnt help to have small grains if theyre not uniform.”Microvaporiza

27、tionElectrical discharge machining using a sinker EDM is another micro-holemaking option. Unlike , which create small holes for threading wire through the workpiece when wire EDMing, EDMs for producing microholes are considerably more sophisticated, accurate and, of course, expensive. For producing

28、deep microholes, a tube is applied as the electrode. For EDMing smaller but shallower holes, a solid electrode wire, or rod, is needed. “We try to use tubes as much as possible,” said Jeff Kiszonas, EDM product manager for Makino Inc., Auburn Hills, Mich. “But at some point, nobody can make a tube b

29、elow a certain diameter.” He added that some suppliers offer tubes down to 0.003 in diameter for making holes as small as 0.0038. The tubes flushing hole enables creating a hole with a high depth-to-diameter ratio and helps to evacuate debris from the bottom of the hole during machining. One such sinker EDM for producing holes as small as 0.00044 （11m） is Makinos Edge2 sinker EDM with fine-hole option. In Japan, the machine tool builder recently produced eight such holes in 2 minutes and 40 seconds through 0.0