Pre-Plating Vibratory Finishing: the key to a successful electro-plating

Vibratory finishing is one of the major sectors to carry out pre-plating work. Because of low production cost per parts, this process significantly reduces labor-intensive manual work. Die-casting parts, for example, now start from casting machines to the vibratory finisher, and then enter into plating lines without labor involvement.

 

electro plating workshop
electroplating workshop

 

1.   The benefit of Vibratory Finishing in Pre-Plate Finishing

Generally, vibratory finishing machines can deburr, polish and clean metal parts surface. In term of pre-plating vibratory finishing process have 3 major benefits:

 

1.1 Vibratory Finishing Process Remove Grease and Dirt on Parts surface

During production, the surface of the parts will be attached with grease, rust, oxides, dust, and other dirt. These contaminants can seriously affect the contact between the plating parts surface and the plating solution. This made the electroplating reaction difficult to carry out.

Vibratory finishers are the ideal equipment to solve this issue. The degreasing process uses a mild alkali compound to remove greasing substance leave on parts surface.

While the parts tumbling, a mild alkali compound is circulated inside the bowl. The vibratory tumbling media cleans the entire parts surface contour including cavities. The wear debris and dirt are flushed away as the machine tumbling. This process is time-saving and cost-effective.

 

1.2 Vibratory Finishing Process Improve parts surface conditions.

The greater the roughness of the surface of the plated part, the greater is the true surface area. It is difficult to accurately determine the current density used in the plating due to the large roughness, which affects the formation quality and time of the coating, and the convex part and the concave part.

The current distribution of the parts is inconsistent, and the resulting coating is not uniform, and even various defects occur.

Therefore, unless the plated part itself requires a certain roughness, the surface of the plated part should be smoothed as much as possible before plating to ensure the quality of the plating.

 

1.3  Vibratory Drying Process Cleaning Parts Prevent Rusting

Because most pre-plating finishing processes are water-based. So we need to come up with many ways for parts drying and rust inhibit.

The most common drying method is a centrifuge with forced hot air. This process is best for small parts. However, this process leaves parts with an oxidation layer, especially for zinc parts (Zamak). When the parts have slots that retain water, it is best to dry the parts in the corn cob vibratory dryer. When the corn cob is kept hot enough, it absorbs the water quickly without sticking to the parts.

2.  Hand-on tips to improve Plating Quality with Vibratory Finishing Pre-Plating Treatment

The metal parts before electroplating sometimes create orange peel that show up only after electroplating process. To inspect the parts imperfection that hidden under the polyester media matte finish, we recommend using a pencil eraser to remove the matte.

 

  1. Media Hardness: Use a softer media because a harder media may damage parts surface. Polyester plastic tumbling media is the most common media for pre-plating treatment. Plastic tumbling media with less abrasive content is softer.
  2. Media Size: Use a smaller size media as its support and cushion parts better.
  3. Parts on Parts damage: If put too many parts in the vibratory bowl, parts may hit each one and leave damage on the surface.
  4. Water level: More soap and water will cushion the movement.
  5. Machine Tumbling: machine runs too aggressively leads to parts hit. We suggest using variable frequency drive to slow down vibratory tumbling action.
  6. Additional Step: Improve parts surface condition with an additional vibratory process.

3. Case Study

a) Aluminum machining parts

 

aluminum machining parts before and after deburring
aluminum machining parts before and after deburring

 

AL 6061 is smoothed perfectly with general cutting plastic tumbling media. We choose tetrahedron shape plastic media to deburr aluminum parts slots. A tetrahedron can access slots and cavities nicely without lodging in problems. The part after deburring is ready for electroplating. Besides, the processing time is about 30 minutes and only a small fraction of time compared with hand buffing.

b) Zamak3 die casting parts smoothing

 

Zamak3 die casting parts vibratory finishing
Zamak3 die casting parts vibratory finishing

 

The photo above shows the parts before zamak3 parts from die casting to the finished product. We can see from the photo that the mold is in good condition.

Firstly we use ceramic media to remove the defect from the die casting process. This process takes about 3-4 hours in the vibratory finishing machine depending on parts surface quality.

The second step is to use plastic media to reduce surface roughness. This process continuous 2-3 hours depending on the surface condition. If you still want to improve the surface further, we can use zirconia ball to polish the parts.

The right part is the electroplating parts. It is ready finished item for market.

 

zamak parts before deburring
zamak parts before deburring

 

The photo above is another example of zamak3 parts. However, we can see from the above photo that the parts mold condition is not good. So it leaves heavy mold ling to the parts which need to remove manually. We recommend improving the mold quality so we can reduce process cost afterward.

4. Conclusion

In this article, we discussed 3 major benefits of vibratory finishing improving electroplating performance. Firstly, pre-plating treatment removes grease and dirt on parts surface. Secondly, pre-plating vibratory finishing improves surface conditions. Thirdly, vibratory drying process absorbs water residue on parts surface. All these factors significantly improve plating quality.

In the second section, we shared some practical tips to improve Plating Quality with Vibratory Finishing Pre-Plating Treatment.

In the last section, we show the performance of parts before pre-plating treatment.