Increasing Forging Die, Tool Life, Increasing Yield and Preventing Rejections using Japanese Cold-Welding and other Proven Protective Coatings

Mr. S.P.Shenoy
M-Tech. Met-Engg.


Steel Plant Specialities LLP
211, Raikar Chambers, Govandi East, Mumbai-400088. India.
Contact: 9820493373/ 91-22-67978060 / 25552459

Mr. Srikar P.Shenoy

Abstract and Introduction:

Protective Coatings continue to play a major role in increasing productivity and reducing costs in metal forming and treatment processes like hot forging and heat treatment. This technical paper presents details and successful case studies of three such protective coatings:

  1. Die, mould and tool wear are major reasons for production downtime and increased costs in most industries. Carbide coating to protect only the wear-prone areas of dies using Japanese cold-welding technology is a practical and economical technique that has proven to increase die, mould and tool life. This technique, though similar to welding, does not pose difficulties of smoke emission, pre and post-weld heat treatment and requirement of skilled labour. It can also be carried out on the die or tool without unloading it from the forging press or such equipment, without need of a weld shop.
  2. When forging die is in use, it is mandatory to keep it well lubricated and the die temperature maintained as per required application. Die protective coating cum lubricant is used to achieve these objectives. Graphite-in-water formulations are popularly used as die lubricants until recently. Though effective as a lubricant, graphite is highly polluting and dirties the surroundings. Effective white lubricants using environment friendly materials are now developed that have proven to eliminate graphite and associated pollution. Substantial increase in die life and reduced pollution is possible by the use of white lubricant cum protective die coating.
  3. Oxidation and resultant scaling at high temperatures is caused during heating of billets, ingots for forging and during heat treatment of formed components. Scaling leads to enormous losses by way of rejections of produce, reduced yield and increase in non-value adding operations like shot-blasting, grinding, pickling, etc. These parameters are becoming increasingly sensitive in open and closed die forging, especially of expensive grades of steel like SS, Nickel-bearing steels and aerospace forgings. Anti-scale protective coatings can be used to prevent or substantially reduce high-temperature oxidation and scaling.

These techniques can be easily adopted by all metal forming units, big and small.

Subject 1: Increasing forging die life by the use of Japanese cold-welding technique.

Problem: Die, mould and tool wear are major reasons for production downtime and increased costs in most industries. Apart from using the most appropriate die steel, a few effective treatments can be administered to dies to increase their service life.

Observation: Most of the forging dies wear out only in certain areas. The complete die impression does not wear out at once. Only sensitive portions of the die, like edges, profiles that take majority forging load, etc. wear out much faster than the rest of the die profile. Some examples are shown below:

Technology: Carbide coating using Japanese cold-welding technique involves coating of tungsten carbide on selective wear-prone areas of dies/ moulds / tools through the special electronic Japanese Cold Welding Technique.

Cold welding is carried out as a ‘Preventive Maintenance’ technique on new dies. It is a surface hardening technique, similar to nitriding, but is administered manually using the cold-welding equipment. Hardness of tungsten carbide layer deposited by cold-welding on dies can surpass nitriding to reach hardness of more than 70 HRC.

Benefits of Japanese Cold Welding Technology:

  1. Skilled welders not required. Can be carried out by anyone
  2. Open space / ducting not required. No fumes are generated during cold welding
  3. Time saving process as dies need not be removed from forging equipment
  4. Pre and post welding heat treatment not necessary. No stresses are generated during cold welding as it is a cold process.

Additional benefits of Japanese Cold Welding Technology:

  1. Nitriding of dies not required. Hardness of tungsten carbide coating is more than 70 HRC, which is higher than hardness obtained by nitriding process (62-64 HRC).
  2. Increased die life due to high wear resistance.
  3. Substantially reduced maintenance downtime of dies and tools.
  4. Ability to coat selective areas of dies that are prone to wear. Process does not require the complete die to be treated/ protected.


Carbide coating is seen as silvery, coarse coating on wear-prone areas of dies:

Substantial increase in die life after cold-welding:

S. No. Description of die / tool Metal Forming Equipment Not coated die life

(No of parts formed)

Japanese cold-welded die life(No of parts formed) Percentage of increase in die life
1. Sheet metal pressing die & tool set Sheet metal press(cold pressing) 18500 25900 40%
2. Hot forging die 1000 tonhot forging press 4000 5400 35%
3. Hot forging die 1000 tonhot forging press 8000 12000 58%
4. Hot forging die 1600 tonhot forging press 10000 15900 62%
5. Hot forging die 1600 tonhot forging press 10000 22000 120%


Observation after implementing Japanese cold-welding technique: Demonstrations of this technique have shown encouraging results. Hence, there is no risk in terms of die/ tool breakage or reduced life. The percentage of increase in die and tool life has varied from as low as 35% in initial trials to as high as 120% in recent trials. Various parameters that contribute to success of this technique are well documented, leading to refinement of the technique.


Subject 2: Increasing die life using customised die lubricating equipment and environment friendly die lubricants.

Die lubricants play an important role in achieving optimum die life.

Problem: Use of cheap oils when used as die lubricant leads to very low die life and pollutes the forge shop. Water miscible graphite based lubricant is better than oils. However, graphite spreads around and makes the forge shop dirty. Being good conductor of electricity, graphite damages the electrical equipment of modern forging presses.

Observation: Many times, switching over from oil to water-based graphite or to synthetic lubricants is daunting. This is due to improper spray techniques, leading to low die life or die breakage as depicted.

Technology: New generation synthetic die lubricants that are effective and clean are now available. Synthetic die lubricants have often proven better compared with graphite. This is possible only when synthetic lubricants are used with correct method of spraying. Customised spraying systems and sprayguns, depending on the specific forging profile need to be used.

Fig 1: Reduced forging load by using lubricant. Ref.: Dr. A. S. Deshpande, IIT, Mumbai, India.

Case Study I: Productivity Improvement due to reduced die grinding time by switching over to graphiteless, water soluble lubricant.

Sr.No. Particulars Graphite BasedDie Lubricant


GraphitelessDie Lubricant


1. Forging Equipment 1000 Ton Press
2. Product Forging Sleeve
3. Dilution Ratio 1 : 10 1 : 10
    4. Time Loss Due to Die Grinding at Each Shift 1.5 hours NIL
5. Production in3 shifts 7000 9000
6. Productivity Improvement




 Case Study II : Cost Saving due to graphiteless, water soluble forging lubricant.

Sr.No. Particulars Graphite Based Imported Lubricant Graphiteless Indian Lubricant ESPON
1. Forging Equipment 1000 T Press
2. Product Two Wheeler Crank Shaft
3. Total Production 100 Tons
    4. Consumption of lubricant per 100 tons 400 kgs.
5. Cost of lubricants per kg. $ 3.39/- $ 2.20/-
6. Cost comparison oflubricants per

100 tons

(cost per kg. x 400 kgs.)

$ 1358.00/-


$ 883.00/-
7. Saving per 100 tons $ 475.00/-


Observation after implementing new generation synthetic die lubricants: Substantial increase in die life is possible by the use of environment friendly die lubricants when correct spraying equipment and spraying techniques are implemented.


Subject 3: Reducing rejections and increasing yield using anti-scale protective coatings.

Problem: Oxidation and resultant scaling leads to pit-marks and rejections. Non-value adding operations like shot blasting, grinding, etc. are costly and time consuming.

Observation: Oxidation and scaling are a function of time, temperature and the thermodynamic affinity between oxygen and metal. Recent developments in highly oxidation-prone grades like nickel bearing steels, high speed steels and stringent customer demands do not allow for scale pits, uncontrolled decarburisation and bad surface finish.

Excessive scaling on billets (above) cause pit marks and rejection on forgings as shown in adjacent image.

Technology: Anti-scale protective coating is applied on billets or components to be heated before charging them into furnace. This anti-scale coating acts as a barrier between oxygen and metal. Care is taken to apply a uniform, impervious layer of coating by brushing, spraying or dipping.

Use of anti-scale protective coatings on billets during heating for forging and again on forgings during heat treatment have proven to substantially reduce scaling, control decarburisation, improve surface finish and increase yield. Photos below show substantially reduced scaling on billets. As a result, forged parts do not have scale-pits and have acceptable surface finish.

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Observation after implementing anti-scale protective coatings: Benefits proven by the use of anti-scale protective coatings are:

  • Substantially reduced scaling. Reduced rejections due to scale pits.
  • Shot blasting / acid pickling time is either reduced to a great extent or eliminated.
  • Consistently controlled decarburisation.
  • Increased yield.


Forge shops are assured of increased productivity and substantially reduced costs in hot forging and heat treatment processes by the use of protective coatings like:

Anti-scale protective coatings of billets and forged parts

Synthetic lubrication of dies and

Cold-welding of carbide on dies

A number of esteemed forge shops in India and abroad have adopted these techniques to increase die and tool life, eliminate pollution and substantially reduce forging costs.

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