Machining steps and set-up times reduced

Over three years, new CNC machines have significantly improved set-up and/or cycle times and/or reduced the number of machining steps required to complete trailer components.

Lancashire-based trailer manufacturer, Indespension, has over a period of three years significantly upgraded its in-house machining facilities using Daewoo CNC machine tools supplied by Mills Manufacturing Technology.

In all cases, installation of the machines has significantly improved set-up and/or cycle times and/or reduced the number of machining steps required to complete the components concerned.

Founded in 1968, Indespension has grown to be one of the UK's leading supplier of trailers and allied components.

In addition, it operates the country's largest trailer hire fleet.

The company manufactures trailers for a wide range of specialised activities including boat transport, plant and vehicle transport, van-type trailers for general purpose use and tipper-trailers for the building trades.

It also supplies trailer kits and components for self-build trailer projects.

Production is centred on the company's factory at Horwich, near Bolton, while sales and service is in the hands of a UK-wide network of depots.

Other than raw materials, light fittings, bearings, wheels and tyres, trailers are entirely produced in-house.

Part of the company's success arises from the wide variety of specification and format that this enables it to offer.

In some cases the Daewoo machines are second generation replacements for existing CNC lathes.

However the most recent installation, a Daewoo ACE H400P horizontal machining centre, replaced a largely manually operated production line that machined the coupling head and coupling body for connecting and securing the trailer to a tow-ball.

The machine was supplied as a turnkey package with fixtures and tooling for all of the part variants.

"We have three basic castings for the coupling head and two for the bodies," explained machine shop supervisor, Dave Westhead.

"The latter require seven drilled holes, two tapped holes and one through bore.

We previously needed four separate operations to produce the part and the batch would be machined sequentially.

The ACE does all of the operations in one set-up, apart from a short drilling operation which is completed by the machine operator.

This is much faster, so lead time on a typical batch of 150 parts has reduced from three or four days to one day." It is a similar story on coupling head machining, where a four-sided fixture houses two components per face.

The components require separate drilling and boring operations so each machining cycle allows four completed components to be off-loaded.

Whereas two single part fixtures are used for the coupling bodies, requiring the twin pallet change facility on the ACE to be used, the high productivity available with a single four-sided fixture allows Indespension to achieve its coupling head production requirements.

"Both fixtures are designed to adjust for any component derivative," Mr Westhead revealed.

"It is quite a simple process to change them over although we try to organise production so that changeovers are minimised.

So far as tooling is concerned, the 40 tools permanently resident in the magazine cover all of the current component variations.

The machine has through-tool coolant which gives good tool life on what is predominantly a drilling and tapping cycle." Adjacent to the Daewoo ACE are a pair of Puma CNC lathes from the same Korean manufacturer, a 300M and a 350M, used for brake drum and towing eye machining.

Next to them is a Puma 250M equipped with a short bar magazine used to machine stub axles, while a fourth Puma, this time a specially adapted 350M, is used to machine the ends of square section solid axles.

"We produce a very wide variety of axle and brake drum assemblies," said Mr Westhead.

"For instance, there are 42 different programs on the Daewoo 250M alone, utilising round bar from 32mm to 60mm diameter." Depending on the type of hub used, the axles may have parallel or tapered stub ends.

Each has two bearing diameters that are held to +/-12 microns and finished in their as-turned state to a high standard.

The axles also have a threaded end that takes a castellated nut, and the powered tool facility on the turret is used to drill the cross hole that locates the cotter pin for securing the nut in position.

The Puma 350M for solid axle production performs a fundamentally similar operation.

However, in this case the stub ends are machined on the end of a square section bar of variable length which passes through the spindle tube and is supported by a bar support unit and a specially adapted 3-jaw chuck.

"We used to machine these parts on a centre lathe and locate them on centre with a 4-jaw chuck," Mr Westhead recalled.

"However, set-up was very time consuming as the bar needed to be clocked into position.

On the Daewoo machine, Mills proposed that we use a 3-jaw chuck with a cut-out on one jaw to make the gripping operation self centring.

It works very well and allows us to machine each stub end completely in one operation rather than two or more." As with axles, there is an equally wide variety of brake drums.

In this case the precise diameter is on the cup which accepts the outer ring of the taper roller bearing assembly.

Its diameter must be held to +/-12 microns while the inner friction surface of the drum is held to +/-0.1mm.

Finish is highly important on both.

Drums are machined in two operations.

The Puma 300M is set up for both Op 10 and Op 20 while the Puma 350 M is dedicated to Op 20.

The reason for this is the disparity in the length of the two operations.

Op 10, completed in 55 seconds, locates the drum on the outside diameter.

It face-machines the periphery of the rear of the drum, bores the centre and skims the friction surface.

Op 20 takes 110 seconds with the drum located on soft jaws gripping on the friction surface.

It comprises facing of the front surface of the drum, boring the front bearing diameter and drilling and tapping the holes for the wheel locating studs.

The normal procedure is to complete Op 10 for the batch and then re-set the machine for Op 20.

"The Pumas are a marked improvement on our previous machining methods," Mr Westhead concluded.

"These modern CNC machines are much better than our older equipment, particularly in respect of their ability to perform 'second operation' milling and drilling as part of the main machining cycle.

Similarly, the capability of the ACE H400P to get through more work while simultaneously improving quality is a major step forward.".

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