Many clients are confused about the metal casting production process and production leading time, so they do not know when they should place the orders.
Casting Production Process
Currently, in China, the most iron castings will be made by sand casting process, the most of steel castings will be made by lost wax investment casting process, and shell molding process.
Shell molding process is a type of sand casting process, which is usually used for making iron castings, but now, some steel foundries are trying to use it to produce steel castings too.
Before batch production, the foundries need about 30 to 45 days to make the metal patterns and samples. After sample approval, then the patterns could be used for batch production. You could call this time as the project initial time, or tooling time.
Casting Production Lead Time
Normally, when we receive the orders from clients, we will discuss with our production dept. to assure when we could start the production, and how long we will need to complete them. Then, we will get the production lead time.
There are many production processes affecting the lead time, so it is difficult to say how long we may need. Sometimes, if our production is not busy, and the defective rate is low, then the delivery time will be short, however, if our production is very busy, or there are some quality problems, then the delivery time will be longer than normal.
For the batch production, the foundries will need to go through these processes.
1. Arrangement Time
When we receive the order, we will discuss with the production dept., so they will check when they could start the production for this PO. Normally, the molding machines will be busy for the existed orders, all orders need to queue up.
For this process, normally, 10 to 20 days will be needed. If the order is very urgent, we may arrange it to jump the queue, so to shorten this waiting time. However, this is only for urgent situation. All clients are important for us.
If the orders are continuous, or clients could give us a demand plan, then this process will become unnecessary, because we could arrange the production schedule in advance.
2. Molding Time
For the shell molding process, we need to use molding machines to produce the sand shells and cores, which could be called as sand molds. For the lost wax investment casting process, we need to make wax molds. For the moulding machine process, also known as the green sand molding process, sometimes, we need to make some sand cores too.
For this process, normally, 7 days will be needed. If the order quantity is large, our workers will keep making the sand molds, these existed sand molds will be moved to the next process.
3. Metal Melting and Cooling
After the sand molds completed, we will use electric furnace to melt the pig iron with alloys, or melt steel materials, then pour the melted metals into the sand molds for iron castings, or pour the steel into treated wax molds for steel castings.
The melting process is very short. We could melt 30 tons metals each day. The liquid metals will stay in the sand molds or wax molds, till cooled naturally.
4. Sand Blasting and Grinding
After the cooling process, we will use sand blasting equipment to clean the sand residue on the metal castings, then we will grind the castings to remove the extra materials, parting lines, gating heads etc., then do the second sand blasting again.
Grinding castings is very hard and dirty works, so all foundries are facing the shortage of skilled grinding workers now. Therefore, this process will need some days.
5. Machining Process (if necessary)
After cleaning process, if the castings need further machining works, then we will move the castings to our machining workshop.
It is difficult to say how many days will it take, because it will depend on the machining complexity.
6. Painting and Coating Time
If the castings need painting, hot dip galvanizing, powder coating etc., then we will move them to the professional coating workshops in our local. We could do the spray painting in our foundry, but we have to entrust the other coating works to the professional coating workshops.
Normally, the spray painting will take some time, because it will need time to be dry, but for other coatings, the time will be shorter.
7. Quality Inspection and Packing Time
We will do some quality inspection during production, but after all works completed, our inspectors will do the final quality inspection, including all dimensional inspection, material and defects inspection. After quality inspection, we will pack the casting products for delivery.
Normally, the quality inspection will need 1 to 3 days depends on the result of sampling inspection.