Here's a demand curve for a particular family of products, what is the most efficient way to calculate kanban quantities for its components? any suggestions (for in-house manufactured parts only)

Kanban is a signal to replenish/produce depending on your kanban size and replenishment time. From your graph it appears you need to produce 500 per month as your customer demand. Assuming 20 working days per month that equals 25 per day assuming you build 25 in 8 hours you have a approximate TAKT of 18 minutes. Say you have a part with a standard package quantity of 5 and a replenishment time of 3 hours or 180 minutes. Say you signal when you open package. You send the signal you will produce 10 units before you get replenishment so you need two standard packages line side due to replenishment time. If standard package size changes or replenishment time changes the number of kanbans change. If you change your TAKT times the kanbans will also change. Changing your TAKT times upsets so many things in lean facility that is the last thing you want to change.

Ideally you want to produce or replenish all components one for one based on demand. Think of having a supplier of multiple parts on your products supply a kit of parts to make a single unit, and the kits delivered on a Just in Sequence manner.  

thanks Bill,
I'm familiar with the workings for kanban,
but as you can see there a downward trend is the total numbers. My concern how you setup quantities so that when you have a spike in demand it does not creat stockout, at the same time not inflate you component inventory?.

You have to work with your suppliers and make them lean also. They would build to demand but again I have to warn you changing the TAKT is the last thing you will want to do. Working more hours or even adding another shift could be in the realm of possibilities. You will have to understand your business and have built in capacity for the larger volumes. You may not man for the higer volume thus reducing the labor cost but if you need greater capacity you may have machines sitting waiting for the higher order volumes.

Is your company a build to order company or a build to stock company? A build to order company is leaner than a build to stock company but if you are seeing very spikey demands you may want to build to stock if you can prior to the high volume periods.