The fierce market competition has caused some contractors to spend a lot of effort to find some machining operations which are difficult to process but which can bring profits. National Jet (Lavale, Maryland) is such a contractor.
The company has been engaged in the contracting business of mechanical processing for 67 years. According to reports, it has a reputation for micro-drilling, capable of machining tiny holes as small as 0.001 inch (one-third the diameter of human hair). The ability to machine metal parts with up to thousands of tiny holes has earned the company a lot of business in the textile and medical device industries because few other companies have the processing capability.
Moreover, most of the parts entrusted to National Jet have been pre-processed by other contractors. So National Jet became a professional cutting company that drilled tiny holes on semi-finished parts.
This seems to be in conflict with the company’s policy of always advocating its own hands-on processing. In general, they are hand-polished cemented carbide micro drill bits. And it uses micro-drilling machine tools that its own company previously produced and sold. At the same time, they also process EDM electrode molds to match a variety of unique inner hole shapes. This is in line with the company's decision to work hard to achieve the goal of processing the entire product, not only limited to hole processing.
National Jet's imported CNC machining equipment includes a Swiss lathe equipped with an air spindle and a vertical machining center that is cooled through the inner bore of the spindle to improve general machining and machining capabilities of micro-miniature holes.
In addition to the micro drilling expertise, the company still attracts a large number of users. It also promotes the advantages of one-time processing: the fastest processing speed, delivery of products, reduction of parts processing and lower production costs, etc. win the entire parts processing business.
National Jet's sales manager Chuck Condor and general manager James Odom have the company's micro hole processing and how to obtain market information from users and further improve production efficiency and economic benefits. The following information is mainly provided by them.
Continuously developing micro-hole processing technology
National Jet was founded in 1937 by John Cupler, the pioneer of micro drilling technology. Many years ago, a foreign drill bit manufacturer gave Cupler the most micro drill bit he had produced and asked if he could produce such a small drill bit. Mr. Cupler answered that their way was to drill a hole in the bit and send it back.
These tiny holes can only be seen under high power microscopes, and the determinants of many micro-drilling holes are similar to those of standard-size drilling. Whenever a new mission is evaluated, National Jet must first determine the most effective hole processing method. This has to a large extent also depend on the type of parts processed, the diameter of the inner hole, the geometrical requirements, the dimensional accuracy requirements and the depth, the batch size of the parts processed, and the original processing methods used.
Manually controlled machine tools equipped with microscopes are often used for research projects, small batch production or only a few micro-holes. Some manufacturers who are dedicated to the development of micro-hole machining tools mostly provide hand-controlled machine tools. This processing method dates back to the 1930s of the last century. Others, although they have been retrofitted with CNC worktables, still maintain the manual feed of the drills. Manually feeding such tiny diameter drills requires skilled workers to feel them by hand. National Jet has summarized many of the experiences of micro hole drilling. “Our skilled worker operator can in fact confirm by 'feeling' whether the micro drill bit has been dulled,†said Mr. Condor.
Figure 1 Microholes have been processed into National Jet's technical expertise.
The illustration is a 0.003 inch diameter human hair, which is a
The 0.001-inch micro drill drills through the illustration.
The boring machining program is used in almost every micro-drilling operation to ensure smooth chip evacuation, ensure the quality of micro-holes, surface roughness and optimize the service life of the drill.
Coolant or light oil is used to cool and remove chips from the drill tip. According to Mr. Condor, most flat micro drills produced by National Jet have an aspect ratio (L/D) of 7:1, and 10:1 is generally considered to be the largest ratio that still guarantees tight tolerances.
Drilling a small hole in a surface requires pre-drilling a small blind hole in the part to guide it to prevent the hole from bending or "skewing." Pre-drilled pilot micro drills are generally designed to be very short with a maximum aspect ratio (L/D) of 2:1. The company has a patented processing method that can process micro pilot holes on very sharp workpiece edges.
For high-productivity machining or for parts with many tiny holes that need to be machined, National Jet will use their CNC machining center or lathe. Manual machine tools are often used to perform test drilling on machined workpieces before they are delivered to a new CNC machine. This is mainly to determine the frequency of micro drill tools that need to be changed during processing.
The company’s newly purchased 2215 VMC is manufactured by Fadal Machining Center (hatsworth, CA) and injects coolant through the spindle hole to drill holes smaller than 2.5 mm. This method of machining eliminates the boring method because the chips can be smoothly removed from the cutting zone by the coolant. Even smaller diameter drills can be used on this machine even if there is no coolant channel. The positioning status of the parts can be checked by using a traditional cutting edge ruler or a specially designed straightness tester and the parts can be positioned and adjusted.
The L32 Swiss lathe is produced by Marubeni Citizen-Cincom (Allendale, New Jersey) and provides complete machining of cylindrical parts, including micro-hole drilling in one setup. The lathe has two pneumatic spindles with a maximum speed of 30000r/min, which drives micro drills. Pneumatic spindles are actually more used for precision machining of small-diameter drilling than ultra-high-speed machining. The lathe is also equipped with a bar feeder to provide long-term processing of unmanned parts.
Figure 2 uses a Swiss lathe equipped with a pneumatic spindle for general turning, milling operations and micro hole drilling.
Condor admits that many people are surprised that tiny holes can be processed at relatively low speeds. “We chose to work at spindle speeds of 500-3000 r/min and achieved great success for tiny holes with a diameter of 0.005â€. "Mr. Condor said," In the case of very small feedrates, it is not necessary to machine tiny holes with several thousand revolutions per minute of spindle speed."
The removal of pores after drilling a small hole is an important factor in the completion of the hole processing. Each hole requires the removal of burrs at the hole exit. National Jet usually uses a polished inner hole surface and a manual deburring method that uses a tiny drill bit to remove the burr out of the hole.
National Jet's difficult-to-remove burrs, such as small-diameter oil holes and non-circular holes, are removed using small-diameter steel wire or through EDM equipment. "But for small deep hole processing, we don't generally use EDM because the electrodes are prone to burn the bottom of the hole and produce taper," said Mr. Odom.
Figure 3 Miniature EDM For pipe or other deburring and drilling applications where difficult or impossible to machine.
National Jet's EDM machine can machine tiny holes down to 0.001 inch diameter. In addition to micro-hole machining, the miniature EDM machine can also remove small bits that have been broken into the holes from the parts. The diameter of the drill is very small, so breaking is understandable.
Some company's EDM machines are equipped with a linear motor for rapid movement of the X and Y axis tables. At the same time, it is also equipped with a pallet clamp system to provide quick installation and replacement of parts outside the machine. EDM machines often perform unattended operations throughout the night and on weekends. The latest EDM machine has a PC-based machine control system that enables the original CAM assembly program for CNC machining centers to now be quickly changed to EDM machine processing.
Detection of tiny holes
National Jet does not test every tiny hole on every part. It actually inspects every tiny hole through the Nikon vision system. The vision system can detect the dimensional accuracy and roughness of precision micro-holes, and pass the inspection results to the user via E-mail.
However, for parts that are designed with tiny holes, for example, there are several tiny holes in the spinner head that require high geometric accuracy, which cannot be detected with the Nikon vision system. For this reason, the company has designed a hole that accurately detects the small holes. New method of geometry. In order to check the micro hole geometry and the shape outline of the micro hole, National Jet injected a two-part rubber mud into the hole. When the rubber mud is formed, it will be taken out of the hole. The information on the micro hole profile and geometry etc. It can be obtained by observing a rubber mold under a measuring microscope.
Figure 4 Pre-machined spinner head parts provide very fast parts delivery
Figure 5 Examination of complex micro-hole geometries with rubber mud.
In the past, the accuracy of the geometry of tiny holes could not be checked.
Processed in a single clamping
The strong micro-drilling capability of National Jet has helped the company out of the trough of the recent manufacturing slump. However, the company believes that it must expand this capability to other industrial areas in order to create better business opportunities. “Our tiny hole drilling capability has been successful in industries outside of our initial goals, such as radio communications and the aerospace industry. It can support us in completing many other R&D projects,†said Mr. Condor. “Our focus is still on the ever-growing micro-small parts processing market.â€
The recent economic recession has also renewed its determination to continue moving into the micro hole processing market. Our micro hole machining is often the final processing of the entire part. Or arrange the parts near the final processing. Mr. Odom said that National Jet recently made a lot of efforts to promote the advantages of completing the entire part processing (also called one-time processing) in a single fixture, and purchased a new CNC machining center to pay for its plan. In practical production.
This is always helpful for a manufacturer who has a place in the manufacturing industry to go beyond the professional boundaries and move toward flexibility. The following is a summary of the economic and production benefits that National Jet has brought to users:
â—† Make the product deliver quickly. By having one company complete the processing of the entire part in a single setup, it means that it requires very little transportation and handling, and the processing time is concentrated so that the processed product can be delivered quickly. The first part of National Jet's disposable process was a small-volume vaporizer that required threading and had a key 0.005 inch diameter through hole. The company drilled tiny holes in the parts after finishing all the work steps. National Jet proved to the user that it used only half of the original processing time to process the entire part on a Swiss lathe and finally won the production task for the company.
â—† It is also important to adapt quickly to new product design changes. Rapidly adapting to changes in new product designs, National Jet Corporation, for its major textile industry users, stocks a large number of crude products such as spinner heads. Because blanket manufacturers cannot wait for a new spinner for a month. The company adopted pre-cutting and roughing blanks. Once orders are received, they can rapidly add tiny holes and other geometric features required for the parts to the rough products.
â—† The one-time processing brings high processing precision, greatly reduces the installation error caused by multiple mountings, and ensures the machining accuracy of the parts stably. The user's accusations were avoided in the past because the parts could not meet the specified specifications.
In addition, those user shops that perform overall part production may not consider those important issues in the secondary process, such as the depth of micro drills.
◆ Special experience. National Jet has accumulated a lot of valuable experience in its micro-hole drilling, and it suggests that sometimes through the design of the structure, it can make the process easier and the production cost can be reduced. “If a user needs to drill a tiny hole in a part that is difficult to meet design requirements, it is recommended that the design of the drawing be a transition from a large hole taper to a micro hole configuration, which will make the processing easier and will not affect the product. Performance," said Mr. Condor.
It is important that a company has a fixed professional position in the manufacturing industry. However, the highly professional workshop will quickly find that according to the market needs of users, research and development of new technologies and new processes, providing a variety of technical services for users flexibly, will play an important role in the development of the company. The continued development of this multi-technology service will greatly enhance the competitiveness of companies in the market.
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