General of Project
Project Background
The customer supplied a detailed drawing for a custom heavy-duty dome bolt used in an automotive application. We developed the forging, machining, marking, and coating process according to the confirmed dimensions and surface requirements.
Custom Dacromet Coated Dome Bolts
This project involves the manufacturing of custom dome bolts with Dacromet coating for automotive applications. Dome bolts are commonly used in vehicle assemblies where reliable fastening and corrosion resistance are required.
The bolts are treated with a Dacromet coating, which provides excellent corrosion protection and durability under harsh environmental conditions. This coating is widely used in the automotive industry to improve the service life of fasteners exposed to moisture, salt, and outdoor environments.
Manufactured according to client drawings and specifications, these dome bolts ensure precise dimensions, reliable fastening performance, and consistent coating quality.
Yutung Industrial provides customized manufacturing solutions for automotive fasteners and coated metal components based on customer requirements.
Quantity
200pcs
Material
35CrMo
Surface
The bolts received a Dacromet coating using an NOF Metal Coatings system. The confirmed corrosion-resistance requirement was a salt spray test duration of more than 500 hours.
Process
Manufacturing Process
The dome bolts were manufactured from 35CrMo alloy steel through forging, CNC machining, surface marking, and Dacromet coating.
The production process required control of the bolt head profile, overall length, thread protection, stamped character position, surface finish, and coating appearance according to the customer’s approved drawing.
For custom bolts, shafts, pins, fasteners, and other steel components requiring forging, CNC machining, marking, coating, and dimensional inspection, explore our custom precision metal parts manufacturing capabilities.
The difficulty of the manufacturing:
- Manufacturing Challenges
- The bolt was unusually large, with a head diameter of 50 mm, an overall length exceeding 150 mm, and a single-piece weight of more than 1.2 kg.
- The stamped characters had to be clear, correctly oriented, and positioned according to the drawing.
- The visible head surface required a smooth appearance after machining and coating.
- A special hanging fixture was required to reduce coating marks on the visible surface.
- All specified dimensions and tolerances had to remain within the approved drawing requirements.
Project Process of the Batch
Stage 1: Sampling for one piece without surface coating
We protected the thread in this picture.
We sent these non-coating ball bolts and also the coated bolts for clients to check the size.
We found the problem, that the words are not in the right direction of the drawing.
The word’s direction should be 90 degrees off the flat surface, see above.
There is a dark mark on the top surface.
Stage 2: Correct the word direction
The order quantity is 200pcs. We manufacture all the quantity 200pcs of the forging screw ball bolt body. It is difficult to forge only a few sample quantities because of the material problem.
When we manufacture the forging body of all the ball screw bolts, we predicted that it may have some problems in future. So we make the plus tolerance of the height.
This gives us the possibility to correct the wrong word direction.
If we have the height margin, we remove the words directly and stamp again.
For some heights in which size is not enough, we can not use the above method. We will weld the material to fill the words, and then polish again. After the coating, there will be no appearance difference.
Stage 3- Resolve the Coating Mark problem
We also find the dark tint problem on the surface at the area of “3.5t”. It is the hanging fixture mark when we do the dacromat coating.
We improved the coating craft to resolve the problem.
Stage 4: The word “5mm” area is not clear!
After all, 200pcs is coated, and we found some of the bolts had a new problem. The word 5mm area is not clear.
We use the method mentioned above to do the work. We correct it for one process.
Project Result
The project was completed after several rounds of sample checking and production correction. The final 200 dome bolts met the confirmed dimensional, marking-direction, surface appearance, and coating requirements.
The four-month production process involved close coordination between forging, machining, marking, coating, quality inspection, and customer communication.
For OEM projects involving forged and machined fasteners together with coatings, stamped markings, matching hardware, inspection, or assembled industrial components, explore our broader custom industrial parts manufacturing capabilities.
