MINIATURE PARTS MANUFACTURING REQUIRES TODAY'S TOOLING SOLUTIONS

There was a time when the term miniature-part machining or Swiss automatic work primarily meant turning tiny parts in long runs on dedicated machines.

Typical workpieces only needed turning because, for the most part, they went into miniature rotating machinery.

Their functions were mainly mechanical. Worn-tool replacement and job-to-job changeovers were tedious and time-consuming. Set screws and other clamp parts on the tooling were usually difficult to access and handle, and they had a real talent for disappearing.

Often half the setup or toolreplacement time was wasted teasing a tiny clamp part or insert back into place, or trying to trace where it went when you dropped it.

This is not the case anymore. Increasingly, today's typical miniature part is as likely to be electronic or biomedical as they are mechanical, with more asymmetric features like flats and transverse holes, requiring milling and C-axis or X-axis drilling, as well as turning. Repeat orders more often involve running design changes in the part, forcing changes in how they are manufactured in the first place. In miniature part manufacturing especially, big changes are developing. (Figures 1 and 2) To address these changes, many new Swiss automatics are essentially miniature CNC mill/turn centers. Their tooling borrows some of the best ideas from mainstream CNC tooling to speed metal removal and reduce cutting forces while simplifying tool replacement and changeout. For example, some new tooling for miniature work multitasks in order to reduce dead cycle time, free up turret space and reduce tool inventories. Other new replaceable-tip tools permit in-situ insert changing for immediate restarting with no offsetting.

In addition, most new tooling for cam-type miniature Swiss automatics enables retooling or worn-tool replacement without having to remove the gang plate. (Figure 3) Taking a closer look at today's most advanced tools available for miniature part machining means taking a look at turning, holemaking and milling tools.

TURNING SYSTEM

Iscar's compact Swisscut turning tool system reduces tool interference problems in the crowded cutting area of camtype screw machines and enables easy insert changing from either side panel. There is no need to remove and reinstall the toolholder to change edges. Insert accuracy and robust seat design ensure the necessary repeatability.

Largely because of their in-situ insert changing capabilities, Swisscut turning tools are also proving popular on CNC machines as well.

The preferred insert grade is IC 1008 with TiAlN- and TiNcoated layers with special chipbreakers tailored for miniature work. Users report good success with this combination on carbon and alloy steels, heat resistant alloys, stainless steel and hardened steel, even on interrupted cuts.

A choice for CNC-type machines is the Swissturn tooling family, which features small shank sizes and in-line design with high-positive cutting geometry and very sharp cutting edges. As a result of the low cutting forces generated, Swissturn tools have proven very successful on fragile, thin-walled parts.

PARTING, MULTI-TASKING

Parting is especially tough on tools because of the increased cutting forces and friction involved as the tool approaches the centerline. The solution of choice today for diameters up to 12.5mm (0.492"), is the Pentacut, a pentagonal-shaped tool with a high positive carbide insert on every point. Indexing is possible without removing the tool. (Figure 4) The Pentacut exemplifies two trends in miniature tooling today: multifunction capabilities and the migration from mainstream machining. In larger sizes, and with different insert grades, the Pentacut successfully handles grooving, recessing, chamfering and parting on standard sizes. With a micron- grain IC1008 insert and a high, positive J-type chipbreaker, Pentacut is proving out in the miniature machining world as well.

Figure 2 - Medical part manufacturing requires correct tooling.

For more challenging parting operations and tight spaces, Do-Grip and JetCut tools both feature space-saving pressure seating of inserts (no screws or clamps) and internal coolant delivery to aid chip ejection and avoid overheating of the tool or workpiece.

For combined parting and moderate external grooving, users report good success with Cut-Grip, which enables multi-directional turning and grooving.

Its design helps reduce tool breakage due to lateral forces encountered when generating grooves wider than the insert itself. Longer grooves or profiled grooves will likely require a sturdier tool such as the Iscar Vlock, with a thicker shank and V-shaped insert seat.

For threading, cycle times can be cut with multi-tooth tooling, which progressively generates two or three teeth at a time. The latest example is the indexable-type IscarThread based on triangular inserts with a triple-tooth profile on each edge. The inserts feature positive rake, precision ground edges and a chip deflector on the top face.

OPTIONS FOR HOLEMAKING

The good news in holemaking is that indexable insert drills are approaching solid carbide drills in accuracy and hole quality.

Iscar SolidDrill SCD, available in diameters as small as 3mm (0.118"), and aspect ratios of three and five, can hold tolerances to m7 levels. Solid- Drill SCDR, essentially a drill-reamer available in the same sizes, meets h7 hole accuracy standards. As with all brittle solid carbide tooling, they perform best on very rigid setups and lowimpact continuous-cut applications.

Figure 3 - Retooling can be done without the need for gang plate removal.

Figure 4 - Pentagonal-shaped tooling offers a high positive carbide insert on every point.

For mainstream miniature holemaking and less-than-ideal machining platforms, replaceable tip drills such as the SumoCham offer better economy, plus in-spindle tip change capability. Only the replaceable tip is carbide; the shank is alloy steel which costs much less and withstands impact and vibration loads better than solid carbide. Also, in the interest of multitasking, a single shank can handle a limited range of tip diameters or different tip styles, each optimized for a particular workpiece material: carbon and alloy steel, stainless steel, high temperature alloys, cast iron, and aluminum. The SumoCham drill incorporates all the familiar features of ChamDrill plus Iscar's Sumo Tec surface treatment, improving penetration rates and tool life by at least 40%.

Both drills are available with optional internal coolant delivery that can be extremely valuable for deeper holes.

For deeper holes (on request), the gundrill is also available in diameters as small as 0.9mm (solid carbide).

With today's miniature gundrills able to deliver IT7 and IT9 precision levels, a lot of cycle time can be saved on holes that are peck-drilled. Plumbing for high pressure coolant delivery is required, but most of today's machines possess this.

INTERNAL MACHINING

Also answering trends in multitasking, indexable tooling and ease-of-use is the Passport tooling family for internal machining. The key to the system is a sturdy cylindrical adapter, with different bores into either end, to accommodate two different tool shank diameters. With the adapter securely positioned, it is easy to switch tools for internal grooving, threading, drilling, boring, backturning, profiling, undercutting and small diameter threading.

The thick Passport adapter provides a great deal of support to the various tool shanks that are inserted into it - including the Picco family of miniature boring bars as well as standard ISO boring bars. With the Passport adapter, the unsupported length of the cutting tool is always minimized.

MINIATURE MILLING

To handle the growing demand for asymmetric electronic and biomedical parts, more and more milling is needed. This is why so many miniature machine tool builders have added a milling axis to their products, or even offered fully-equipped CNC mill-turn centers in miniature sizes.

Not surprising, replaceable tip-milling tools in miniature sizes are being introduced. The latest example is the Multi-Master replaceable-tip milling tool. In just a few seconds, while still chucked in the spindle, a single Multi- Master shaft can accommodate tips for shoulder milling, slotting, smallarea face milling, profiling, drilling, chamfering and a variety of rampdown operations.

UPCOMING INNOVATIONS

One of the fastest growing segments of the miniature machining industry is medical parts, especially orthopedic implants and prostheses. The reason is the worldwide population of people over the age of 65, the biggest market sector for implants, is expected to nearly triple by the year 2050.

The main differentiating feature in medical part manufacturing is that 90% of the implant components are made of titanium alloy Ti6Al4V, an unfamiliar metal in this industry. Some stainless steel is used as well, but surgeons prefer titanium because of its strength-to-weight ratio and the fact that human tissue adheres to it better.

Compared with the more familiar ferrous and aluminum alloys, titanium is more difficult to machine. Think of it as stainless steel but with a tougher, stringier chip, plus a strong tendency for break-out at tool entry and exit points.

Carbide tools do not need to be coated because they do not react chemically with titanium as they do with steel, but they do need to be very sharp. Also, to protect against overheating at higher machining rates, PVD-coated grades are recommended.

Already developed for titanium work is a broad line of miniature inserts that by and large fit into the same toolholders as described above. Their main characteristics are very sharp edges and honed or ground surfaces to produce a fine finish and deny a foothold for built-up edge. Currently, the Iscar lineup of miniature titanium tooling includes an endmill with extremely sharp edges; a bowl shape and honed surfaces; solid carbide drills as small as 0.8mm with P geometry; reamers with S geometry; four types of turning inserts with aggressive WF or MD chipbreakers; and titanium versions of Jetcut parting tools. There is a titanium version of the popular Tang- Grip heavy-duty tangential parting tool within the pipeline.

The bottom line is, given all the new challenges and opportunities facing the miniature parts manufacturers, today's tooling will not hold you back. In fact it will help you move ahead.

Iscar Metals Inc.
Arlington, TX
iscarmetals.com