Product Details Supplier Info More products

C Dugard has recommended a switch from milling-based methods to grinding methods after the introduction of a higher performance folding machine by a long-serving customer at Constant Precision.

Constant’s milling-based method of producing blades and anvils used in the printing industry for automatically creasing and folding paper and card seemed doomed to failure, due to difficulties in maintaining the tolerances demanded by the high-speed machine and because of the projected increase in production output to meet the order demands of the print finishing specialist.

However, Constant undertook a close study of possible methods of manufacture with several machine tool suppliers, and it was C Dugard’s application team at Hove that suggested a switch from milling to grinding.

Following trials on a Chevalier Smart B-1224-II surface grinding machine, the new method more than halved the original processing time for the two ranges of parts required and ensured a high level of quality.

‘A lot of work over the years has involved specialist and often very difficult components,’ said Charlie Constant, managing director of Constant Precision.

‘These have come from the customer’s research and development activities as well as prototyping projects that have led to production batches of up to 1,000 components for the printing, medical and laser, food packaging, construction equipment and security sectors, in addition to the local university,’ he added.

Certain projects outline the skill level of the nine-employee company, such as the complete machining of an engine block and head for a vintage racing Maserati that was worth in excess of GBP1.25m.

Some of these parts were machined on the Dugard Eagle 660 vertical machining centre; C Dugard being a machine supplier with which Constant has developed a close working relationship based on the level of service and support he has received.

So, when facing the problem of the new design of tooling, Constant called C Dugard in to see how the milling process on the OI tool steel components could be improved to enable his customer to reproduce on-the-fly creasing and folding of up to 5,000 folds on 400g/m2 A4-sized material in an hour to a positional tolerance of +0.1mm.

Constant also considered outsourcing the finish production of the blade and anvil; however, when possible suppliers looked at the number of variables in the component dimensions that could cause them headaches, they either priced the job right out of court or immediately declined to quote.

The eight types of matching blade and anvil vary from between 350mm and 500mm long and each is 12mm wide and 40mm deep.

Batch quantity can often run to 200 pairs a month.

Running down the centre of each blade is a raised triangular section just 1mm wide with a critical 0.1mm radius at the top.

Each side of the triangular section has to blend into either a large radius over the 12mm width or a flat face, according to the material to be folded.

The anvil has a 1mm-wide slot with a 0.1mm radius running down its length that has to marry up to and provide a datum for the blade and material to be creased and folded.

Both radii are critical with tolerances having to be held within 0.03mm, and the overall straightness of the grooves and triangular section have to be within 0.05mm to prevent scratching, marking and out-of-position folding of the material factors, which would lead to immediate rejection by the customers of both printer and finisher.

After several discussions with C Dugard, an initial single fixture was devised for the Chevalier machine to produce one part at a time that, once proven, led to a double fixture that would enable two blades or anvils to be ground simultaneously using a paired grinding wheel.

Key to the three-axis CNC grinding machine process was the multi-function programmable control that has variable graphic simulation for grinding and wheel dressing cycles.

This allows the speed of the review sequences to be varied in both forward or reverse by the operator using the machine’s electronic handwheels.

Preset dressing cycles can also be initiated at any time during the grinding cycle without resetting.

This level of flexibility was important to Constant as, depending on his customer’s requirements to cater for unusual or different papers, inks and finishes, the profiles may have to vary slightly – and these can be accommodated with quick and simple adjustment of the program.

With the machine ordered, Constant then faced a problem with its installation – his 2,400ft2 factory in Kempston had no room for the machine so he had to set about finding new premises.

In the interim, C Dugard offered the facility of its showroom in Hove for his setter/operator to develop the process and run production.

While there, C Dugard’s application engineer produced four basic programs including the dressing sequences for the single and twin-wheel setting for the single grinding pass.

This was not straightforward as the grit and grade of the wheel and dressing speeds had to be balanced in order to prevent wheel breakdown on the tight radii set on both component types and also to avoid burning of the component surface.

While lease negotiations and fitting out of the new premises were underway, Constant’s customer then suggested the machine be temporarily installed in its own research and development department.

This would allow the two companies to discuss and try out modified forms on experimental blades and anvils.

It also involved C Dugard in re-siting the machine at the customer, then at Constant’s new facility along with re-commissioning the machine after its move.

Today, with the process developed and in production, by changing from milling to grinding using the Chevalier machine, the cycle time for each blade and anvil has been reduced by almost 60 per cent.

Still working with C Dugard, Constant is developing wheels and improving dressing cycles and their frequency, making full use of the flexibility of the machine’s CNC to further improve the process.

View full profile