In Tune With the Changing Times

During the past two decades, there has been a revolutionary change in the design and production of forgings, especially for the high-volume requirement industry worldwide. In earlier days, forging companies were only forging manufacturers. With the evolution of modern supply chain management, especially in the high-volume automotive parts industry, many forging companies started doing value addition to their forgings for their clients globally.

In the modern industrial world, a forging company, along with being a forging supplier, is also a supplier of either fully-finish or semi-finish turned parts. In several cases, forging companies offer value addition by heat treatment and other finishing operations up to ready-to-assemble stage of components. Further up the ladder are the suppliers of unit assemblies as well. The evolved forging companies now do not stop at the economics of the forging technology to produce raw forgings. They have started considering things on a macro level, including the value-adding first metal cutting operation process.

There is a link between raw forging as it comes out of the forging process and the feeding into the value-adding first operation of turning or turn-milling. Globally, as the automotive parts industry volumes are getting integrated and enlarging with a fewer number of tier 1 and 2 suppliers, there is an increasing need for the automation of workpiece handling even at this first operation stage after forging. The focus is to know about the various types of automatic feeding and handling devices
of workpieces to load on the
first operation chuck and highlight their designing factors relating to the forging quality and material.

Design aspects and practical factors

There are varieties of forgings with illustrations and the practical issues to consider for achieving the highest level of efficiency in a fully automated value-adding first operation. It focuses on the below points:

Automatic handling of forgings for feeding into the first machining process of turning / turn-mill operation

Chucking for the first machining process of turning operation

Machining process (Turning / Turn-Mill Operation)

Automation in turning process is mainly considered for forgings from 0.5 to 25 Kg weight, 30 to 350 mm diameter and 10 to 400 mm length. Turning process of forgings achieving high efficiency of productivity can be broadly classified into:

Automotive sector with high volumes and minimum part varieties

Non-automotive sector with medium to high volumes and medium part varieties

Forging quality vs cost

It is a myth that to achieve a better quality of forging, higher cost is involved in the forging process. On the contrary, better quality of the forgings reduces the cost of machining and automation. The various classification and effects of quality of forging on manufacturing costs are such as:

Dimensional variations (diameter, length / width): Too small or too large variations make the control of the turning process more difficult.

Geometrical variations (taper, step, burr): Small variations make the control of turning process easier than large variations.

Material issues (hard spots, sand inclusions, pin holes): More of such abnormalities in forgings make the control of turning process more difficult.

Quality vs problems vs countermeasures

Forging quality issues lead to several problems. Most obvious problems are directly in the machining process:

More tool passes to remove excess material

Unstable tool life resulting in productivity loss

Longer cutting cycles due to above

Unstable chucking resulting in the workpiece flying out

Ultimately may lead to tool and machine damage.

The simple countermeasure is to sort out the forgings with excessive variations manually and pre-machine the excessive material by low-cost manual machines to bring the variation within controllable limits. Though this countermeasure sounds simple, it involves additional management of machines, manpower and logistics.

More comprehensive countermeasure is sorting of forgings automatically and using suitable gauging system for just the critical dimension, which is directly related to chucking and tooling cycle. The objective is not to measure the actual dimension, but to gauge if the critical dimension of height to diameter is in the allowable limit for efficient handling and chucking. It is also possible to check if the part is being loaded in to the chuck with the correct side in and out. To certain extent it can also be designed for Poka-Yoke.

There are various countermeasures for automation of the feeding-in of forgings to
the first machining process
of turning.

Feed-In devices

There is a variety of solutions possible based on following factors:

Stackability

Round or non-round external shapes

Volume of feed-in stock required: Typically to run unmanned even during lunch breaks of the operator, depending on the TACT time of the line and overall size of the forging.

Standard work feeders

Stacking type: It is suitable for fairly good quality uniform shaped forgings which can be stacked one above the other in the orientation as required for loading into the chuck.

3-Pole centralizing pallet system: For round external shapes

Center pole pallet system: For forgings with smooth round or symmetrical punched bores

Combination of above for uneven forgings

Customized pole pallet system: For non-round and unsymmetrical shaped forgings where orientation is required to load the forging into the chuck.

Flat non-stacking type: This is suitable for forgings which cannot be stacked easily. One or more forgings are set into special jigs on a square pallet for the loader to pick up by a special palletized program.

Feed-In conveyors

Flat belt or Mesh conveyor

Pitch-feed conveyor

Parts Feeder – Vibratory bowl feeder

Magnetic picker type for direct setting of forging bin

Chucking and machining issues

Chucking surface

There are several effects of forging design on chucking and machining. The most common chucking surface is the outside diameter of the forging or in case of larger forgings, sometimes inside diameter. If this chucking diameter has a large draft angle or step due to forging die mismatch etc., standard straight action wedge type jaw chucks are not suitable for safe chucking.

The effect on machining mainly would be interrupted cutting affecting tool life. Most    common chuck type is universal ball lock type chuck with centralizing action. Cylinder stroke is sensed by proximity switches to ensure that forging is clamped properly. Locating surface

If the locating surface has a large taper or burr, it results in uneven stock removal in first chucking process which in turn affects the subsequent chucking processes and may result in uncleaned surfaces. The effect on machining is again interrupted cutting affecting tool life. If the locating surface is not too rough, location sensing system with air pin-hole check can be used. Bore with / without pre-punching

Many designers want to reduce forging cost by avoiding punching out the bore. If the face is straight, drilling operation can be easier but most of the forgings are with a dimple in the center.  In such cases special drilling tool may be required, which increases machining cost and cycle time as well. On the other hand, if punching is done with too much stock removal left or eccentric punching, can have adverse effect in rough boring operation. Especially if bore length to diameter ratio is high, stable rough boring may not be possible or special boring bar has to be used, again resulting in more cost and cycle time.

Types of chucks for forgings

A variety of chucks are commonly used for the first operation chucking of forgings in turning process.

Standard wedge type chuck: Even though this is low cost, it is suitable for only very good quality forgings where defects mentioned earlier are non-existent.

Long stroke chuck: This is basically the standard chuck with longer jaw strokes. If chucking diameter surface is good but there is burr at the back which must be avoided, this chuck can be useful.

Universal ball lock chuck (centralizing): This is probably most commonly used chuck for forgings, especially for automation to ensure proper chucking. It can take care of a certain level of forging issues as mentioned above.

Swing jaw chuck: For forgings where face clamping is required, this chuck is useful in automation.

Universal ball chuck (compensating) with center location and tailstock: For shaft forgings with pre-forged or pre-machined faces and centers, this type of chuck is required.

2-Jaw, 4-Jaw or 6-Jaw chucks: For odd shaped forgings and specialized applications, where automatic loading and unloading has
to be coupled with automatic chucking, such options are available.

Wrap up

In the global perspective of raw materials, forgings, initial machining process, finish machining process, sub-assemblies and final assemblies, quality and cost are no more independently controllable. To achieve the objective of the final assembled product to be globally marketable, all the links in the supply chain – machine tool suppliers, logistics suppliers – must work together. Equipped with the global know-how and expertise, Muratec has so far been consistently achieving its goals of providing full turnkey solutions to suit local needs and working environments, and hence, enjoys a leading position in the manufacture and integration of turning technology and automation.

AUTHOR

K Raghunandan

Marketing Advisor

Murata Machinery Ltd Japan

k.raghunandan@nan.muratec.co.jp

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