Cleaning forged parts is a crucial step in the manufacturing process. It directly impacts the quality of the product, the efficiency of further processing, and even the lifespan of the equipment. During forging, high temperatures and pressure can cause scale, burrs, and other impurities to form on the surface of the work piece. If these contaminants aren't removed, they can affect the appearance, accuracy, and physical properties of the part. So, choosing the right cleaning method to get rid of these surface issues is key to improving the quality of the forging. In this article, we'll take a closer look at the cleaning methods used at different stages of the forging process, discussing the pros, cons, and best use cases for each.
Pre-Forge Cleaning Methods
Before forging, the main goal of cleaning is to remove scale from the surface of the hot billet. This ensures the mold fits accurately and the final product has a smooth surface. Here are some common cleaning methods.
1. Wire Brush, Scraper, and Scraping Wheel Cleaning
Using a manual or mechanical wire brush, scraper, or scraping wheel to scrub the surface of the hot billet is a simple and effective way to remove scale. These tools are easy to use and work well for cleaning smaller or more complex-shaped billets.
2. High-Pressure Water Cleaning
High-pressure water jets are used to directly hit the billet's surface, removing scale with the force of the water. This method is gentle on the surface and is great for large-scale production.
3. Descaling During Forging
Sometimes, the forging process itself helps remove scale. As mechanical force is applied during forging, some of the scale is scraped off. This step not only clears away scale but also smooths out the surface, setting up a better base for the next steps in the process.
Post-Forging Surface Cleaning Methods
After mold forging or heat treatment, it's important to clean off any remaining scale or other impurities to ensure a clean surface and smooth subsequent processing. Here are some common methods for post-forging cleaning.
1. Tumble Cleaning
Tumble cleaning involves placing the forgings and abrasive media (like sand or stones) in a rotating drum. The abrasives collide with the forgings and scrub off the scale and burrs. This method is simple and effective but can be a bit noisy. It works best for forgings that are not too hard on the surface and can handle impact.
2. Vibration Cleaning
In vibration cleaning, the forgings are placed in a vibrating cleaning unit along with abrasives. The vibrations cause the abrasives to rub against the forgings, removing scale and burrs. This method is better than tumble cleaning for more delicate surface treatments and prevents excessive wear.
3. Sandblasting Cleaning
Sandblasting uses high-pressure sand or steel shot to blast the surface of the forging, removing scale with high-speed impacts. This method is great for forgings that require precise surface treatment. However, it can create a lot of dust, and the process tends to be slower and more expensive. It's typically used for forgings that need special technical attention or for certain materials.
4. Shot Blasting Cleaning
Shot blasting uses high-speed rotating blades to launch steel shots at the forging, which removes scale by impact. This method not only removes scale but also strengthens the surface, improving fatigue resistance. It's great for boosting the part's strength, but it can sometimes hide surface defects. So, for critical parts, additional inspection methods like magnetic or fluorescent tests are often needed to ensure no hidden flaws.
Chemical Cleaning Methods
Acid cleaning is a common chemical method that removes scale through a reaction with an acid solution. This process generally includes steps like degreasing, acid corrosion, rinsing, and drying. Acid cleaning works well for cleaning surfaces and revealing any flaws. It's ideal for forgings that need a high-quality surface finish. However, acid cleaning can leave behind a rough, black residue on the surface, and the waste acid can cause environmental problems. Proper disposal of the acid solution is required to meet environmental regulations.
The Impact of Acid Cleaning
While acid cleaning is effective at removing scale and improving surface quality, the waste liquid can pollute water sources. As a result, relying too heavily on acid cleaning in industrial settings should be avoided. For situations where cleaning is needed without environmental pollution, mechanical methods like shot blasting are often used alongside acid cleaning to achieve better results.
Friction and Surface Changes During the Cleaning Process
Friction plays a significant role in how the forging surface turns out. The friction environment in forging is different from traditional mechanical friction. During forging, the workpiece can experience pressures ranging from 1000 to 2000 MPa at the mold contact points. Scale forms on the surface, and the friction forces are closely tied to this process. Scale can act as a lubricant, but when it touches deformed metal, it can negatively affect the surface quality.
As new metal surfaces are formed, the old scale is destroyed, and friction increases. If lubrication is insufficient, this can lead to more friction, which could result in "plowing" marks on the surface or even metal transfer, damaging the surface quality. Therefore, it's important to ensure proper lubrication during forging to keep the surface smooth and prevent issues caused by friction.
Conclusion
Cleaning forgings is a vital step to ensure quality and smooth subsequent processing. Each cleaning method has its strengths and best use cases. Choosing the right method can help remove scale, burrs, and other impurities, while also improving the mechanical properties and appearance of the forgings. However, in real-world production, it's essential to consider factors like material type, surface requirements, production costs, and environmental considerations when selecting the appropriate cleaning method. With the right cleaning process in place, the performance of the forgings can be significantly improved, ensuring they perform at their best in the next steps of production.
