Very few resources will teach you the practical process planning done in industry. If you are looking for details of what goes inside process planning of typical process then answers are below.
Let us consider that you have to manufacture a cricket bat. This example is taken to understand the basics easily and the same can be applied to any complex product.
Before starting a process planning one important thing which you should ask for is what is the production volume requirement?’ This means in a day/ or a year how many bats are to be manufactured. Let us assume your company produces bats and you need 100000 per year. You need to check the production days in a year leaving aside all the holidays and weekly off. Suppose your company has around 300 working days out of 365 then you will get the per day requirement of 100000 divided by 300 i.e. 333 per day approx.
Once you understood the daily requirement, the next question is what is the production per hour. If you are working in one shift and let us assume you have around 7.5 working hours approx. leaving aside lunch/tea break of a typical 8-hour shift. This will give you per hour requirement. In our case 333 divided by 7.5 ie 44 bats per hour approximately. This is also called as jobs per hour(JPH).
Now you know that you have to produce 44 bats per hour, you can calculate TAKT time. 60 min. divided by 44 gives 1.36 min for one bat. So every 1.36 min. one bat should be produced and 1.36 is called as TAKT TIME.
Suppose typical cricket bat can be manufactured through four processes such as cutting the profile of bat from raw material, shaping to size, polishing, applying stickers and all the processing takes around 30 min. then you will need 30 divided by 1.36 ie 22 stations approx. (assuming you deploy one person per station)
If you increase the manpower then probably you can reduce stations only if all the persons on that station can work independently. Let us assume that two persons can work simultaneously then you can deploy two people per station and 30 divided by ( 2 x 1.36 ) will give you 11 stations. This 30 min. is called as work content. Work content is the total time required to produce a particular product. If there is a sequence of processes which can not be done in parallel then you can not add extra manpower to reduce stations.
So in entire calculation TAKT time is important to allocate correct manpower to avoid over or under production. Overproduction is an inventory and form of waste. If there is a sudden decrease in market demand then overproduction is cost wasted. Underproduction is simply not meeting the demand and sometimes require working in two shifts rather than one shift to meet the demand. This is inefficiency in production.
There are a couple of other key factors such as following
% Utilization:- If a person is working on a station for complete 1.36 min. That means cycle time of that station is equal to TAKT time then it is 100% utilization. If your cycle time is less than takt time then remaining time is waste on that particular station.
% Value added work:- In the entire process, only value addition on part comes under this %. All other motions such as picking, placing, unwrapping, moving come under non-value added work. Suppose there is a process of cutting the raw material to its shape then only cutting is value added. All other motions are non-value added. This % is a measure to reduce wastes in motion, packing, unwrapping, adjustment etc.
If the process of cutting takes 1 min out of 1.36 min cycle time then 1 divided 1.36 will be 73.5% value added. % value addition can be improved if other movements are reduced and thus increasing productivity.
Hope above explanation gives an idea of process planning to layman or beginners.
Note:- There are various small important factors in the above calculations which are not discussed here. These process specific details can be discussed separately.