GlossaryKind of term: Manufacturing termProcess chain
What is a process chain?
A process chain is the full sequence of processes that turns raw stock into an accepted part, including the steps carried out at suppliers.
Where a step takes place does not decide whether it belongs: work done in house and work done at a heat treater or other supplier are part of the chain alike. For a hardened shaft that might be: saw the bar, rough turn, harden and temper at a heat treater, grind and inspect. The term stresses how the steps connect: each link receives the part in the state the previous one left it in.
How do the steps in a process chain connect?
The order of the chain sets allowances, material condition and risks. If you grind after hardening, you leave grinding stock when you rough turn; how much depends on material, size, heat treatment and the distortion to expect. A heat treatment or coating can shift dimensions, and an anodic or electroless nickel layer has a thickness the preceding machining allows for; an anodic layer also grows partly into the surface and partly onto it. Residual stress from the stock and from roughing can be released as distortion during hardening; whether stress relieving after roughing is worthwhile depends on it. Changing one step can therefore change the requirements on the others.
How does a process chain work in practice?
As long as the steps do not overlap, the lead time of a chain is the sum of processing, transport and waiting times at every link. With subcontracted steps the waiting often weighs most, for example at a heat treater that fills a furnace only once there is enough work. Cost also sits between the steps: transport, packaging, incoming inspection, an extra setup after hardening to re-establish a datum. A quote that counts only your own operations leaves those items out.
What is a process chain often confused with?
A process chain is not the routing: the routing is the list of operations with work centres and times that takes an order through the company, and it can include subcontracted steps as lines; the process chain describes the technological order and how the processes interact. Nor is it the digital thread: the thread is the data that travels with the part, the process chain the physical steps.
How do you see a process chain in Blake?
In Blake a part's own operations sit as separate lines in the estimate, with material, machining, setup and programming. Subcontracted links, such as hardening, anodising or coating, each get their own line from your subcontract library. If the price of such a link is missing, the line stays open rather than counting as zero. More on estimating.
Frequently asked questions
What is the difference between a process chain and a routing?
The routing is the list of operations with work centres and times that takes an order through the company. The process chain describes the order of all processes, including those at suppliers, and how each step affects the next.
How do I price subcontracted steps in a process chain?
As a line per step at the supplier's price and any minimum charge per batch, with the waiting time in the lead time. Also price the in-house steps the subcontracting triggers, such as an extra setup after hardening or an inspection after coating.
Why is the lead time of a process chain hard to predict?
Because it is made up of all processing, transport and waiting times, and the waiting time at each supplier can vary from week to week. The more subcontracted links, the more uncertainty in the lead time.
How much stock should I leave for hardening?
It depends on material, size, heat treatment and how much the part distorts. Your heat treater and measurements from earlier batches give a guide value. Leave the stock only on the faces you grind or re-turn after hardening.