Machining composite laminate material: Care needed

Drilling

Standard twist drills can be used with laminates, but it is advisable to vary the point angle to accommodate the thickness of the material. The angle needs to be such that the total diameter of the drill has fully entered the hole before the point breaks through the material. 

Prevention of any ‘lifting’ of laminate layers can be achieved by removal of the positive ‘rake’.  The land also needs to be removed to improve flow of the swarf and this is best achieved by using the ‘woodpecker’ method to clear any surplus.

When making large holes in a sheet, a wing or fly cutter can be used with a small ‘pilot’ hole for easy guidance. This also applies to ‘trepanning’ which can be carried out with standard wing trepanning cutters.

Holes that are to be subsequently tapped should be drilled to be slightly oversized on the core diameter and any open ends chamfered. The material’s natural resilience will cause a hole to close in slightly when the drill is withdrawn.

Approximate speed guide for high speed steel drills

Drill diameter	Revolutions per minute	Feed
1.5mm	7,500	0.15mm to 0.20mm per revolution
5mm	2,500
6.4mm	2,000
12.7mm	1,000
19mm	700
25.4mm	500

Gear cutting

Laminates offer an excellent solution for manufacturing gears and ‘teeth’ can be cut with normal tools on a milling machine or a gear shaper. Speeds and feeds will vary depending on the shape and size of the teeth, but 43mm/min is a good average peripheral speed when using a high speed milling cutter. The feed should be reduced to 15m/min when cutting steel shrouded gears. If securely clamped and backed, unshrouded gears can be cut in banks if required.

Grinding

Centreless grinders are best when working with tube or rod sections and using an average diameter reduction of 0.25mm is advised. Grinding wheels must be kept clear from clogging and the surface should be regularly ‘trued’.

Guillotining

A powered guillotine can cut laminate, however care should be taken with the maximum thickness levels versus the moving blade angles. 

Recommendations for Guillotining

	Maximum thickness	Blade slope
Paper based laminate	1mm	4mm in 1m
Fabric based laminate	2.4mm	20mm in 1m
Glass based laminate	2.4mm	20mm in 1m

Milling

Plain or universal millers can be used with laminates where a considerable quantity of material is being removed. For smaller amounts, spindle moulders can also be used.  Use cutters with straight or spiral teeth for a smoother finish.  Ensure that ‘tooth pitch’ does not exceed 16mm for a 100mm diameter cutter. A maximum depth of cut of 15mm and cutter surface speed of 1200 to 1830m/min should be used.

While these are the most straightforward methods, when more complex machining is needed, the laminate manufacturer can advise on how to achieve a successful result.  Tufnol can either give guidance on actual techniques and equipment or can provide expert machining services to deliver the best outcome for customers.

Top Ten Machining Tips

Being competent at machining in general is half the battle to achieving good results when working with laminates, but there a number of important tips that will help ensure a good result.

• To begin with, ensure tools are kept sharp at all times – this may seem obvious, but it is surprising how quickly tools can become blunt and this will cause heat generation and deliver a poor surface finish.  
• Always make sure ample clearance is allowed so that only the cutting edge is in contact with the working surface. Where possible, keep tools reserved for specific applications, particularly where components are to be used in electrical situations where a more precise result is required.
• Tools made from high speed steel will always produce the best possible finish, particularly for small production runs, but Tungsten carbide tipped tools will give a better and longer life. For glass reinforced grades of laminate, carbide tips are suitable for small scale work, but where large amounts of machining are necessary, diamond tipped tools will always give the best result.
• Always keep everything swarf free, particularly when drilling and tapping. Clogged up tools will only generate yet more heat and use of the ‘woodpecker’ technique will avoid any problems.
• Generally, high speeds with slow ‘feed’ offer the best result – again as this avoids too much heat generation. A lighter finishing cut will give a good surface finish and a light cut at all times is advisable.
• Use backings or supports to prevent any deflection due to the pressure on the tool.
• Backing with a similar material will deliver a perfectly clean edge across the layers.
• In most situations, it is recommended that laminate is machined dry, but if a particularly fine finish is needed, using a very small amount of light mineral oil can be applied. When machining for electrical component use care should be taken on using any kind of lubricant as it can impair electrical current in some cases.
• One of the disadvantages of dry machining is dust generation and extraction equipment must be used to alleviate this.
• Tufnol’s Health & Safety publication contains all the information needed to ensure safe machining.