What is the optimal quantity of raw materials to purchase and the best timing for procurement?

Determining the optimal quantity of raw materials to purchase and the best timing for procurement involves several steps:

1. Forecast Demand: The first step is to forecast the demand for your product. This can be done using historical sales data, market research, and industry trends. This will give you an idea of how much raw materials you will need to meet this demand.

2. Evaluate Lead Time: Lead time is the time it takes for your supplier to deliver the raw materials. You need to factor this into your planning to ensure you have the materials when you need them.

3. Calculate Economic Order Quantity (EOQ): EOQ is a formula used in inventory management that determines the number of units your business should add to inventory with each order to minimize the total costs of inventory—such as holding costs, order costs, and shortage costs. The EOQ formula is: √(2DS/H), where D is the annual demand, S is the order cost, and H is the holding cost per unit per year.

4. Consider Safety Stock: Safety stock is a buffer of inventory that you keep to protect against variability in demand and lead time. The level of safety stock you hold will depend on how risk-averse your business is.

5. Implement a Reorder Point (ROP) system: The reorder point is the level of inventory which triggers an action to replenish that particular inventory stock. It is a minimum amount of an item which a firm holds in stock, such that, when stock falls to this amount, the item must be reordered.

6. Regularly Review and Adjust: Market conditions, demand, and supplier reliability can all change, so it's important to regularly review and adjust your purchasing and procurement strategies.

Remember, the goal is to have enough materials to keep your production running smoothly without tying up too much capital in inventory. It's a delicate balance and may take some trial and error to get right.