Tri star university machining plastics 2016

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MACHINING PLASTICS

Rev. 2016a



Before we begin machining plastics we should understand that it is not “the cheap stuff.”

Most plastic material is more costly than metals in $/cubic inch.



PVC 0.5UHMW 0.6NYLON 6/6 1.0ACRYLIC 1.2ACETAL 1.2PET 1.4ABS 1.4POLYCARBONATE 1.8NORYL 2.2STEEL 2.3POLYSULFONE

3.7BRONZE 4.4

Relative Costs of Materials ULTEM PEI 4.8

POLYETHERSULFONE 5.4STAINLESS STEEL 6.7TEFLON PTFE

7.1 KYNAR PVDF

9.1RULON LR 16.9TECHTRON PPS

17.8PEEK 25.1RULON J 25.7TORLON PAI

30.5POLYIMIDE 79.5CELOZOLE PBI

101.4



Having established that plastics can be costly it becomes important to understand what we are dealing with before beginning any operations.

THERMOSETTHERMOPLASTIC

Plastics are also broken down into two subcategories of amorphous or crystalline. This

molecular structure is very important to the performance properties of any plastic material.



Thermoset plastics are given one chance to liquefy and take a shape. Once that happens the

part can never be changed, at least through a melt process.

Phenolic EpoxyPTFE Micartas

Melamines

Often thermosets are used with fillers or as part of a composite.

Thermoset Laminates



Thermoplastic materials represent the largest class of plastics

• These materials melt and reform without chemically changing.

• The list is long and quite diverse and is complicated by the fact that identical materials

have multiple trade names.

• In some cases the trade names are better known than the generic designation.

Nylon Pellets



Most plastics that are machined are thermoplastics

• All thermoplastics melt within a range of 250-650F.

• If enough friction is developed during machining, the plastic will melt.

• The key to successful machining of plastics is controlling the heat.

• Plastics have higher thermal expansion than metals so they will grow at a much faster rate.



ABS (CYCOLAC)Acetal (Delrin)AcrylicNylonPolycarbonate (Lexan)PolypropylenePolysulphonePolyvinyl chloride (PVC)Polyester (Estralon & VALOX)UHMWPolyphenolsulfide (Ryton & Techtron)

CTFE (Halar & Kel-F)PPO (NORYL)PEEKPFAPVDF (Kynar)Q200.5 (cross-linked styrene)ETFE (Tefzel)PAI (Torlon)PEI (Ultem)PI (Vespel & Meldin)PBI (Celazole)



Each thermoplastic has its own melting point and characteristics.

Added to this is the potential addition of fillers:

Glass fibersCarbon fibers

GraphiteCarbon

Molybdenum disulfidePTFE



Material Melt Temp °F

Coefficient of Expansion 10EE-5/°F

Flexural Modulus10EE-3 PSI

Notched IZOD Ft-Lb/In

Water Absorption %

ABSAcetalAcrylic

Nylon 6/6PolycarbonatePolypropylene

PolysulfonePVC

Polyester PBT/PETHaylarNorylPEEKTorlonUltem

PolyimideTeflon

UHMWRytonPBI

225330176360300336358170240258250320530410530600266275815

45.4*

4.83.85

3.12.93.34

3.82.61.73.12.65.5362.71.3

375400

*14034521039021027518035053073048047580

172550950

32

0.40.9170.81.2

0.751556

1.62.71

1.53320.50.5

0.350.240.31.7

0.150.020.3

0.050.08

00.070.5

0.330.250.240.010.6

0.050.4



General Considerations• Use positive tool geometries with ground peripheries.

• Carbide tooling with polished top surfaces for maximum life. Diamond tools or polycrystalline tooling for optimum

surface finish on polyimides.

• Use adequate chip clearance to prevent clogging.

• Adequately support the material to restrict deflection from the tool load.



Drilling

More heat is generated in drilling than in any other operation.

• Twist drills with twist angles between 12 – 18°. Large flute area assists in chip removal.

• Cutting lip should be ground so one edge is .005” to .010” longer than the other.

• Use blunt angles (115° – 130°) for thinly walled pieces to prevent expanding the OD.

• Small dia. (1mm – 25mm) high speed steel are generally sufficient.



Drilling Large diameter holes, 25mm or larger• Slow spiral (low helix) drill or general purpose bit ground to a

118° point angle with 9-15° lip clearance is recommended. Lip rake should be ground and the web thinned.

• Best to drill a pilot hole using 600-1000 rpm and a feed of 0.005-0.0015 per revolution.

• Secondary at 400-500rpm at 0.008-0.020 feed to expand the holes.



Drills must be sharp to reduce friction.• High speed is acceptable for many unreinforced materials.

• Carbide is required for reinforced materials and some unreinforced plastics.

• Coolants are usually necessary and retracting drills for chip removal may also be needed.



Drill Sizes Hole diam.No. 60 thru 33No. 32 thru 17No. 16 thru 01

5,0003,0002,500

1/161/83/161/45/163/87/161/2

5,0003,0002,5001,7001,7001,3001,0001,000

A thru DE thru MN thru Z

2,5001,7001,300



For larger diameter holes spade drills may be used.

• Usually in 1 inch increments.• Used to enlarge pilot holes to finished sizes.

To hold larger parts make a truing cut on the OD at the chucking end.

• Will prevent excess stress.• Jaws should be radiused.

• Chuck as lightly as possible.



TurningTurning tools should be relieved to reduce rubbing.

• O-5 degrees negative• Back rake recommended

Keeping cutters exactly on center is important.

High speed tooling is generally not acceptable. Carbide tools honed with fine grit (400 to 600) diamond

wheel.

Diamond tip tools are frequently used for long runs.



Material Hole diam. Feed (In/rev)Acetal 1/16 to 1/4

1/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Acrylic 1/161/81/41/23/4

1 to 2+

.002 -.005

.003 -.010

.005 -.012

.008 -.015

.015 -.025

.020 -.050

Teflon 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Polyethylene 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Depth of cut Speed FT/Min Feed (In/Rev)

0.150.025

500 – 600600 – 700

.010 - .015

.004 - .007

0.150.025

450 – 500500 – 600

.005 - .010

.004 - .007

0.150.025

350 – 500500 – 600

.010 - .015

.003 - .008

0.150.15

500 – 600500 – 600

.010 - .015

.004 - .007

Drilling Turning



Material Hole diam. Feed (In/rev)PVC 1/16 to 1/4

1/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Polystyrene 1/161/81/4

1/2 to 3/41

1.5 to 2+

.003 - .007

.004 - .008

.005 - .010

.008 - .012

.010 - .015

.015 - .020

Nylon 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

PEEK 1/16 to 1/41/2 to 3/41 to 2+

.002 - .005

.004 - .008

.008 - .012

Depth of cut Speed FT/Min Feed (In/Rev)0.150.15

500 – 600500 – 600

.010 - .015

.010 - .015

0.150.025

200 – 300350 – 400

.015 - .010

.002 - .005

0.150.025

500 – 600600 – 700

.010 - .015

.004 - .007

0.150.025

600 – 1000600 – 700

.010 - .016

.004 - .007

Drilling Turning



Material Hole diam. Feed (In/rev)PET/PBT 1/16 to 1/4

1/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Polycarbonate 1/16 to 1/41/2 to 3/41 to 2+

.002 - .005

.004 - .008

.008 - .012

Polysulfone 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Techtron PPS 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Torlon 1/16 to 1/41/2 to 3/41 to 2+

.007 - .015

.015 - .025

.020 - .050

Depth of cut Speed FT/Min Feed (In/Rev)0.150.025

500 – 600600 – 700

.010 - .015

.004 - .007

0.150.025

500 – 600600 – 700

.010 - .016

.004 - .007

0.150.025

500 – 600600 – 700

.010 - .015

.004 - .007

0.150.025

100 – 300250 – 500

.010 - .020

.005 - .010

0.025 300 – 800 .004 - .025

Drilling Turning



Material Hole diam. Feed (In/rev)Ultem 1/16 to 1/4

1/2 to 3/41 to 2+

.007-.015

.015-.025

.020-.050

Polypropylene 1/161/81/4

1/2 to 3/41

1 1/2 to 2+

.003-.007

.004-.008

.005-.010

.008-.012

.010-.015

.015-.020

UHMW 1/16 to 1/41/2 to 3/41 to 2+

.007-.015

.015-.025

.020-.050

Depth of cut Speed FT/Min Feed (In/Rev)0.15

0.025500-600600-700

010-.015.004-.007

.15.025

200-300350-400

.015-.010

.002-.005

.15.025

500-600600-700

.010-.015

.004-.007

Drilling Turning



Plastics are also flexible materials.• Work pieces flex and often must be supported.

• Materials compress at the point of cutting and then return.

• Thin walled parts often change during machining without returning to size.

Solutions include special supports, proper choice of the sequence of operations, tool

geometry, and tool materials.



Cut-off Tool Designs



Plunge cutting is commonly used in screw machining plastics.

• The width of the tool should be less than the min. diameter of the work piece.

• Feed rates are determined by the stiffness of the stock o.oo4” to 0.010”/revolution

• Serrated cams can interrupt chip ribbon.

• Slow feed rate near the end of the travel and do not dwell at termination to produce best finish surface.



Chip removal is also a special problem with plastics.

• Some materials produce chips that wrap around parts and spindles.

• Melting of chips onto work surface can occur.• Some materials produce abrasive chips which can

damage machinery.

Solutions include high pressure coolants, vacuum chip removal systems, tool geometry, chip breaking cycles, serrated cams, and sometimes you just have to stop

and clean the machinery.



Tapping & Threading

To reduce tearing of first few thread:• Reduce spindle speed

• Chamfer prior to tapping• A leadscrew threading attachment can be used

Threading may be cut with single point tools• Class I and II usually done in one pass

• If final pass is needed - cut depth of 0.007” to 0.010”

Self-opening die heads tend to tear the threads.



Plastics are “notch sensitive”. Sharp V threads are not recommended.

For best results use: Whitman

American Standard unified

For tapping holes use high speed oversized taps:

H-3 for smaller diametersH-5 for larger diametersMust be extremely sharp

For deep tapping (3:1):Enlarge flutes

2 flute taps



Removing Burrs

Creating burr free parts is always a goal• Selecting operating sequence

• Tool geometry

Tumbling operations with ceramic media• Some materials are very tough (nylon).

• Some materials are fragile when walls are thin. • Test a few pieces before establishing a cycle.



Coolants are generally not required for most plastic machining

If coolants are desired, consider the following:

• Flooding with water-soluble oils, light cutting oils and mist sprays are used to reduce heat build-up and to flush chips.

• Materials that absorb water, particularly nylons, must be watched to be sure • dimensions are stable.

• Use of petroleum based fluids can cause cracking and crazing of amorphous materials like acrylic, polycarbonate, Ultem PEI, Polysulfone and Radel.



Vertical milling using face mills, shell mills, end mills, and fly cutters is common.

• Holding fixtures that eliminate flexing are often necessary.

• Chatter marks can result from part movement or chips being pulled over the machined surface.

• Burrs can be reduced by running the tool beyond the end of the part onto a harder surface.

As always, sharp tools with good clearances are necessary.



When sawing plastics dissipation of heat is the major problem.

Conventional radial and swing saws can be used.

Circular saws are ideal for straight cuts from sheet; band saws are preferred for irregular or curved

shapes.

Never use a blade that has cut metal or other abrasive materials.



Sawing Tips• Band sawing is versatile for straight, continuous curves or irregular cuts.

Table saws for straight cuts and heavier thicknesses can be done with adequate horsepower. Blade style should be selected based on material

and surface finish desired.

• Rip and combination blades with a 0° tooth rake and 3-10° tooth set are best for general sawing.

• Hollow ground circular saw blades without set will yield smooth cuts up to 3/4” thickness.

• Tungsten carbide blades wear well and optimize surface finish.



To cut heavy plate, Hss buttress or skip-tooth blades are preferred.

At least 2 teeth should be in contact with the piece.

Circular saws should use hollow ground blades with a set.

Carbide blades provide the best wear.



A steady even feed rate is really important.

Fast feeds result in binding or machine stalls or breakout.

Light feeds result in heat build-up and melted material in the saw teeth causing binding.

The best results are obtained with an adjustable power feed.



Notes of CautionHolding forces - because plastics deform, chuck and collet forces must be minimized and/or spread over as much area as possible.

Material relaxation - deformation caused by machining forces does not always recover instantly. Pieces should be rechecked for size

after sitting 5-10 minutes. Some close tolerance parts with thin walls must be rough machined, allowed to sit overnight, and finish

machined the next day.

In extreme cases, the material must be annealed prior to machining, a blank machined, reannealed, and finish machined.



Machining difficulties and causes – Drilling 1DIFFICULTY COMMON CAUSES

Chatter 1. Too much clearance2. Feed too light3. Drill overhang too great4. Too much rake

Feed marks or spiral lines on inside diameter

1. Feed too heavy2. Drill not centered3. Drill ground off-center

Oversize holes 1. Drill ground off-center2. Web too thick3. Insufficient clearance4. Feed rate too heavy5. Point angle too great



DIFFICULTY COMMON CAUSESUndersize holes 1. Drill dull

2. Too much clearance3. Point angle too small

Tapered holes 1. incorrectly sharpened drill2. insufficient clearance3. feed too heavy

Burnt or melted surface 1. wrong drill type2. incorrectly sharpened drill3. feed too light4. drill dull5. web too thick

Chipping of surface 1. feed too heavy 2. clearance too great 3. too much rake

Machining difficulties and causes – Drilling 2



Machining difficulties and causes – Drilling 3DIFFICULTY COMMON CAUSES

Holes not concentric 1. Feed too heavy2. Spindle speed too far3. Drill enters next piece too far4. Cut-off tool leaves nib5. Web too thick6. Drill speed too heavy at start7. Drill not mounted on-center8. Drill not sharpened correctly

Burr at cut-off 1. Cut-off tool dull2. Drill does not pass completely

through piece

Rapid Dulling of Drill 1. Feed too light2. Spindle speed too fast3. Insufficient lubrication



Machining difficulties and causes - Turning and boring 1DIFFICULTY COMMON CAUSES

Melted Surface 1. Tool dull2. Insufficient side clearance3. Insufficient coolant supply

Rough Finish 1. Feed too heavy2. Tool improperly sharpened3. Cutting edge not honed

Spiral Marks 1. Tool rubs during retreat (use the same fall on cam as rise)

2. Burr on point of tool



Machining difficulties and causes - Turning and boring 2DIFFICULTY COMMON CAUSES

Cracking or chipping of corners 1. Too much positive rake on tool2. Tool not eased into cut 3. Dull tool4. Tool mounted below center5. Sharp point on tool

Chatter 1. Too much nose radius on tool2. Tool not mounted solidly enough3. Material not supported properly4. Width of cut too wide



Machining difficulties and causes - Cutting off 1DIFFICULTY COMMON CAUSES

Concave or convex surfaces 1. Point angle too great2. Tool not perpendicular to spindle3. Tool deflecting4. Feed too heavy5. Tool mounted above or below center

Nibs or burrs at cut-off point 1. Point angle not great enough2. Tool dull or not honed3. Feed too heavy

Burrs on outside diameter 1. No chamfer before cut-off2. Tool dull



DIFFICULTY COMMON CAUSESMelted surface 1. Tool dull

2. insufficient side clearance 3. insufficient coolant supply

Rough finish 1. Feed too heavy2. Tool improperly sharpened

Spiral marks 1. Tool rubs during retreat2. Burr on point of tool

Machining difficulties and causes - Cutting off 2



Machining plastic components is a skill any good shop can develop if you recognize:

• Most plastics melt, and care in generating heat is important.

• Each plastic material has characteristics that differ from other plastics.

• Plastics can be highly abrasive.

• Plastics can be very expensive.

Remember to always use sharp tools !!!!



About TriStar Plastics Corp.TriStar is a leader in the engineering, fabrication and manufacturing of high-

performance polymers, composites and self-lubricating bearing materials. But what truly sets us apart is our commitment to service and customer care; we are dedicated to

helping you find the best material for your demanding application.

Our capabilities include everything from initial design, material section and prototype, right through to production and we do it all in-house. We are a proud partner to over 50 industries, including agriculture, construction, marine, railroad, military and medical, and

we offer a wide selection of stock and custom-fabricated self-lubricating bearings.

At TriStar, our goal is to become your in-house plastics engineering department.

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Tri star university machining plastics 2016