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The Challenges and Benefits of Implementing a CNC Grinder

Oscar Bautista
Click here to see this story as it appears in MODERN CASTING.

With the technological development in today’s metalcasting industry at its advanced worldwide level, it’s important to take full advantage by applying the technology to metalcasting’s complicated processes. Automation has become more flexible, allowing it to be integrated in almost all industries. That’s key because manufactured products are requiring higher quality and high demand.

Fimex (Guadalajara, Mexico) has been committed to making a foray into state of the art technology in the field of casting and machining. It has more than 50 CNC machines, such as lathes and machining centers, a fully automated chrome-plating plant that is one of the most modern in Mexico, robotic arms for buffing and polishing process lines for brass and bronze parts, an automatic pouring system for bronze castings, and now the first CNC steel castings grinder machine that has been installed in Latin America.

The grinding and finishing processes have been historically one of the most difficult to show high efficiency values in the metalcasting industry due to the nature of the process itself.

CNC technology has been used in machining processes for several years and has evolved greatly in a very short time. Today’s CNC machines are robust and flexible, allowing them to be used as a CNC grinder for steel parts, while grinding and cutting tools simultaneously to remove the excess material in castings.

Although this technology of grinding machines already exists, few companies manufacture and distribute them globally, and few metalcasting facilities take advantage of it. In Fimex’s case, it’s with a variety of machines of this type as well as completely automated manufacturing cells for casting.

Justifying CNC
Fimex is a steel and bronze casting and machining company. The steel division represents 70% of the company and its primary market is in low- and medium-sized parts distributed in several market niches.

To discuss why this purchase was justified, it is necessary to mention some of the advantages and disadvantages CNC technology brings to grinding.

Advantages:
Precision.
Repeatability.
Quality.
High security in the process.
Ability to pre-machine surface areas of parts.
Ability to handle big batches of production.

Disadvantages:
Limited dimensions and size of parts.
Weight-limited parts.
Costs of machinery and tools.

Flexibility, productivity and quality are added-values of automatic grinding, and with this in mind, and after analyzing its primary market niche, Fimex felt the CNC grinding would be a profitable option. Fimex had the opportunity to buy a second-hand CNC automated grinding machine in England that was in very good operating condition. This and the benefits of the machine resulted in a return of investment of five years.

The CNC grinder has a maximum part size of 20.5 in. (520mm) and maximum part weight 242.5 lbs. (110 kg). The maximum swinging diameter is 23.6 in. (600mm) with four natural axis of operation. There’s a dust extraction system and up to three cutting tools.

The three strongest points of CNC grinding focus on:

Flexibility: By having two work tables of rapid change, parts can be loaded and unloaded while the machine is operating. This reduces the risk of the operator and increases productivity. Quick changes of holding fixtures becomes easy and fast to switch for different parts since the system changes the entire pallet, making it quick and productive.

Strength and precision: The machine has been designed and manufactured to work with grinding materials such as steel, which makes it robust and reliable, ensuring a long life machine operation and highly precision parts.

Quality: Having a system that measures parts using a laser gives the ability to verify the current position of the workpiece and compensate for errors due to the dimensional variation of the parts and fixtures. This maintains the quality and tolerance required.

Implementation
Once the decision was made to buy a CNC grinder, the challenges began.

The first involved adapting the new technology to a manual process considered one of the most difficult and complex in the metalcasting industry.

To achieve the optimal implementation, it was necessary to consider high-capacity personnel required to operate, program, maintain and give support to this equipment. This forced Fimex to make a structural change in the layout of its cleaning facility by connecting it to the machining facility through a door, placing the CNC grinder between both facilities. This means the machining staff could support the operation, and the raw castings would be fed through the cleaning department and continue through the normal process.

The location of the CNC grinding machine gave Fimex good results by reducing material movements and time, obtaining an optimal process time.

Once the machine was installed and the operators and technicians had been trained, Fimex began the development of the holding fixtures and the grinding programs.

For the selection of parts to grind automatically, Fimex considered relevant criteria such as: quantity of production (weekly, monthly, yearly), dimensional tolerance and surface finishing, size and weight of the part, difficulty of surface grinding, and families of products otherwise known as similar parts.

So far, Fimex has developed more than 20 different fixtures for more than 30 different parts. Some of these are flexible and functional for similar parts, and others are designed for a specific part number with different operations due to its complexity.

Throughout the implementation of the CNC grinder, Fimex had several challenges to overcome:

Develop simple holding fixtures designs.
Quick-change of parts.
Robust fastening and repeatability.
Flexibility in part numbers by fixtures.
Grinding programming.
Working with slice number and machine movements to reduce the cycle times.
Achieving high productivity per part number.
Long life of grinding tools with the correct operation conditions for grinding.

One of the cases where Fimex received a great benefit has been with three part numbers that have similar conditions. In one of the parts, the finishing tolerance required by the customer was +/-0.5mm in width and in parallelism. That previously had forced Fimex to machine the part in a CNC machine to achieve the required measurements, making the product more expensive to process, with the arrival of the CNC grinder, Fimex could lower the cost of the product by eliminating most of the hand work, unifying it in a single operation.

In a second case, two family products with high volume had very close tolerances. With a complex surface on this part, the hand grinding was slow, complex and generated a high rate of re-work and scrap. Once the plant processed this part in the CNC grinder, Fimex achieved high productivity and quality in both products thanks to the repeatability of this process.

Fimex has seen the benefit of using a CNC grinder for finishing on high production parts, high quality and highly complex parts, allowing it to become increasingly competitive and offer higher quality products to the international market. Now Fimex is prepared for the future when the economy reactivates and high production returns.

Still, Fimex is continuing to look every day to make this process more efficient and integrate a greater amount of parts to take full advantage of this new technology.  

This article is based on a paper presented at the 2015 National T&O Conference. It is being used with permission from the Steel Founders’ Society of America.

 

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