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Cutting remarks for laminate machining

Cutting remarks for laminate machining

Choosing an incorrect machining technique can cause heat build-up, resulting in a poor surface finish

Tufnol Composites’ managing director, Roy Thomason offers his advice on the top five most common machining methods for laminates.

When it comes to machining high pressure industrial laminates there are some basic parameters for machinists to establish. For instance, should laminates perhaps be machined like steel, or aluminium, or thermoplastics?

The answer is actually none of these. Due to the low thermal conductivity of laminates there are a number of techniques that are advisable to consider. Choosing an incorrect technique can cause heat build-up that will result in a poor surface finish and impair the performance of the laminate. Care also needs to be taken in choosing the correct standard form of laminate in order that the laminations are running in the correct direction appropriate for the application.

The first technique to examine is drilling. Standard twist drills can be used with laminates, but the point angle may need to be varied to accommodate the thickness of the material. The angle should be such that the total diameter of the drill has fully entered the hole before the point breaks through the material.

Roy Thomason, managing director of Tufnol Composites

The positive ‘rake’ should be removed to prevent any ‘lifting’ of the laminated layers and the land removed to improve flow of the swarf and this is best achieved by using the ‘woodpecker’ method to clear the surplus swarf from around the finished hole.

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

The hole picture

Holes that are to be subsequently tapped should be drilled so they will be slightly oversized on the core diameter and any open ends chamfered. This is because the materials natural resilience will cause a hole to close in slightly when the drill is withdrawn.

The second technique involves gear cutting. Gears made from composite materials offer an excellent solution to many application requirements and gear teeth can be cut on a milling machine or gear shaper with normal cutters or tools. Required speeds and feeds will vary depending on the shape and size of the teeth, but 43mm/min is a good average peripheral speed when a high speed milling cutter is being used. The feed should then be reduced to 15m/min when cutting steel shrouded gears. If securely clamped and backed, unshrouded gears can be cut in banks if required.

When it comes to grinding laminate, centreless grinders are usually best when working with tube or rod sections. Using an average diameter reduction of 0.25mm is advised.  Any grinding wheels must be kept clear from clogging and the surface needs to be ‘trued’ from time to time.

The fourth technique comprises guillotining. It is possible to cut laminate on a powered guillotine, but it’s important that care is taken with the maximum thickness levels versus the moving blade angles.

Finally, the milling of laminates can be executed on plain or universal millers where a considerable amount of material has to be removed. Spindle moulders can also be used where small amounts of material are to be removed using cutters with straight or spiral teeth, which gives a smoother finish. Care should be taken to 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 1,200 to 1,830m/min should be used.

Machined epoxy glass components for the aerospace industry

These are some of the basic techniques for the effective machining of laminate material and adherence to these principles will ensure a successful result. While these are the more straightforward methods that can be adopted, when more complex machining is needed, it is a good idea to call upon the laminate manufacturer for assistance who can advise on the best ways to meet the specific requirements of a particular job. In the case of Tufnol, the company can either give guidance on actual techniques and equipment or can provide expert machining services to deliver the best outcome for customers.

Being competent at machining in general is half the battle to achieving good results when working with laminates. Ensure your 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 to enable only the cutting edge is in contact with the working surface and 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.

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. Finally, 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.

www.tufnol.com

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