Currently, the tile manufacturing industry is striving to reduce carbon emissions and increase processes efficiency. Castellon Tile aspires to modernize its production and gain market share by becoming an industry leader in this effort. We know the following information for Castellon's tile manufacturing process. 

The Product:

• Tiles are available in a variety of styles, allowing customers to create truly personalized designs.
• Style/color combinations are based on 2 clay bodies (white, red), 2 glazes (clear, blue), and 5 tile patterns; net, there are 20 product types. Each tile has a mass of 375 grams.
• Tiles are packed and shipped in cases of 24 tiles, 9 kg/case net, 10 kg/case gross shipping weight. Each case has tiles of a single product type. The minimum order quantity is 1 case.
• The tiles have three main raw materials viz. Quartz, Clay & Feldspar along with minor (<5%) materials.

Customer Requirements:

• Castellon services ~100 customers including hypermarkets, construction, and remodeling companies.
• Castellon's annual sales is about approximately 60,000 cases per year, nearly 1.5 million tiles/year.
• The sales department offers a 60/30 day forecast to the production control.
• The sales department receives orders from customers which they add to Production Control.
• The customers are offered an order quantity lead time of 30 days and can adjust their order mix for 15 days after placing the order quantity.
• Multiple shipments go out to customers every day.

Production Control (Current State):

• Sales orders are batched by product type to fit the production schedule. Batching by type manages changeovers in the base clay, tile press setup, glaze application, and firing operations.
• Receives orders every day; enters orders in Production Control.
• Generates a weekly schedule for Slurry, Spray-Dry, Tile-Making through Firing, and Packing operations.
• Provides 30-day forecast to suppliers to ensure raw material availability.
• Releases weekly purchase orders for procurement of raw materials from three different suppliers.
• Receives change in orders 15 days before shipment.
• Issues a daily priority list to the production supervisor.
• Issues daily shipping schedule to the shipping department.

Production Process, Current State:

• The production plant works 20 days a month.
• Castellon uses the "wet method" for preparation of granules used in tile manufacturing.
  • The "wet method" of making granules starts with slurry-making in a ball-mill followed by spray-drying. It runs one shift/day, 5 days/week. The spray-dried granules are stored in intermediate silos, one for red clay granules, the other for a white clay body formulation.
  • Granules feed the main tile production line including pressing, glazing, and firing operations; these run together semi-continuously, 5 days/week for 3 shifts. Firing is done in a continuous tunnel kiln.
• Quartz, Clay and Feldspar are delivered in powder form via bulk shipment, totaling ~45 metric tons (MT) per month. An average of ~50 MT raw material powder inventory is stored in silos on site at Castellon.
• A glaze preparation process (not shown in VSM) runs in parallel; under normal conditions, it does not affect timing of the main process.
• There is a packing process after firing. Tiles are unloaded from the continuous kiln, placed on carts and transported to case packing. Cases are stored in a warehouse area prior to shipping.

Making granules (slurry making and spray drying)

Slurry making and spray drying operations are coordinated, first preparing a clay-body slurry and then spray-drying the slurry into granules that are suitable for tile pressing. The coordinated process starts with a batch of slurry prepared in a wet ball mill, then transferred to a drop tank so the next slurry batch can be made using the ball-mill. The ball-milling batch cycle time is one hour. The slurry from the drop tank is pumped to the spray-drying tower and made into granules as the next batch of slurry is prepared. The coordinated process typically runs only one shift per day, and the full system (mill, hold tank and spray-dryer) are washed out at the end of each shift. Typically, only one clay body formulation is made per day - starting with the first batch of slurry (1 hour) followed by 5 hours of production of the same clay body formulation before shutting down for the two-hour washout at the end of the shift.

If two different clay bodies (e.g., red and white) are both required on the same day, the extra washout needed for the changeover means only 2 hours of granule production in a single shift, i.e., one hour of each formulation. This is inefficient considering the ratio of wash-water to granule production.

Slurry-making in the Ball Mill:

• Each tile clay-body composition requires a specific mixture of raw materials.
• Ingredients are weighed and added to the batch ball mill along with water to make the slurry. The ball mill grinds and disperses the raw powders with water, along with minor ingredients (binders and dispersants) to aid spray drying and subsequent tile-forming processes.
• Each batch has 750 kg dry powder plus ~500 kg of water; the slurry solids-loading is ~60%.
• It requires 2 operators to run the process.
• Ball mill cycle time is 1 hour per batch.
• The slurry is pumped to a drop tank which has a capacity of ~2500 kg wet slurry (i.e., it can hold up to 2 batches from the ball mill).
• Clay-body changeovers (i.e., different formulations having different clay color) require a full washout; washout changeovers take 2 hours.
• The combined reliability of the ball mill and transfer to the drop tank system is 90%.

Spray Dryer:

• Slurry is pumped from the drop tank to an atomizing nozzle and sprayed into a drying chamber (aka "tower"). Slurry droplets are dried in a flow of hot inlet air, forming free flowing and compressible granules suitable for forming tiles in a pressing process. The average residence time in the spray dryer is less than one minute.
• Spray drying is a continuous operation requiring 1 process operator. The rate of the dryer is matched with the ball mill, i.e., the dryer converts 1250 kg/hr of wet slurry into 750 kg/hr of dry granules.The drying load is ~500 kg/hr of water.
• Spray dryer changeovers between clay types require a full washout taking 2 hours. (Note, cleaning of the tower and ball mill can be done simultaneously).
• Spray dryer process reliability is 90%.
• On average, there is a total of ~6000 kg of dried granules in two storage silos after the spray dryer, one for white and the other red clay granules. Each silo has a 6 MT capacity, usually kept about half full.

Tile Making

Tile making includes pressing the dry granules into tiles, applying a glaze to the surface, and then firing to form vitreous ceramic tile. The pressing, glazing and firing operations are essentially coupled in a semi continuous production line with no surplus inventory between steps.While we could have mapped the integrated press/glaze/fire operations as a single flow process, we chose to show the individual operations to illustrate the process (see current state VSM). The firing step is done in a continuous tunnel kiln where tiles are loaded onto cars which slowly pass through the kiln, through pre-heat, firing, and cooling ones, taking 18 hours. The kiln is designed for continuous 3-shift operation, having a continuous flow of carts stacked with tile in the process of converting from clay to ceramic.

Tile Forming:

• Castellon makes tile using a dry press method. Clay-body granules are conveyed from the storage silo into a die having the shape and style of the tile, compressed, and then ejected. A semi-automated press is used. Pressed tiles are placed on a belt the goes directly to Glaze Application.
• Process requires 1 attendant with machine cycle time of 8 secs per tile.
• Uptime is at 95%.
• There is a 30-minute changeover in the press to change the die for a different tile style.
• Because of the long firing schedule and the weekend shutdown, the last shift of the week on Friday does not produce tiles; tiles produced during the previous shift continue though the process and are left to cool at the end of the last shift on Friday.

Glazing (application):

• The tile-glazing process is semi-automated with tiles from the press on a continuous belt passing under a sprayed-glaze curtain followed by a drying tunnel that uses waste-heat from the firing process. It requires one operator to monitor the process and runs at a rate that is matched with tile forming. The cycle time for glazing and drying is 30 minutes. Changeover to a different glaze is 30 minutes.
• Uptime stands at 95% for the process

Firing:

• Castellon Industries uses a continuous tunnel kiln having pre-heat (4 h), firing (6 h), and cooling (8 h) zones. The full firing takes 18 hours. There is no changeover for clay body or glaze type. The design throughput capacity of the continuous kiln is 200 kg/h of tile.
• The process requires 3 attendants: one to transfer tile and stack in the kiln cars; one to unload the finished tile, and one to monitor the firing process. Uptime is 100%.
• There is an inventory of ~12,000 tiles before packaging

Packing department:

• Packs 24 tiles per box and stores in the finished goods warehouse. Each case has a net tile mass of 24 x 375 g = 9 kg case.Shipping materials add another 1 kg/case making the gross shipping mass = 10 kg/case.
• Cycle time is 60 sec per case with a packing material changeover time of 5 min for a different style of tile.
• 3 operators work for on 1-shift operation with uptime of 100%

Shipping department:

• Removes cases from finished goods warehouse, which has on average 1000 cases of tile, and stages for truck shipment to customers
• The delivery truck has a 2 metric-ton (1 MT = 1000 kg) capacity and can make 2-3 trips everyday

HW Questions:

1) (10 points) Fill in the data box fields (highlighted) and complete the timeline on the Current State VSM, previous page, also provided as an editable ppt. How many annual inventory-turns does this represent?

2) Castellon Tile is considering converting their process to the dry method for tile manufacturing recently reported by Mezquita et al., capturing energy savings by replacing the current slurry spray-drying process ("wet" route) with mixer-granulation ("dry" route). You are hired to make the new operation more efficient, productive, and unlock capacity to incrementally double the business from the current 60,000 cases/y to as much as 120,000 cases. From a VSM perspective, a robust dry-process route can be configured as a continuous flow operation, potentially enabling flow all the way through tile making. What scale and configuration of dry-granulation do you propose? For example: matching the current wet system with silo buffers; matching downstream tile-making; introduce dedicated lines for each clay body?

a) (5 points) What is the takt through the current tile-making process?

b) (5 points) What would the takt be at 100,000 cases/y?

c) (10 points) Assuming sufficient changeovers to achieve EPE = 1 day (i.e., every tile variant can be produced over 3 shifts of tile making), describe two bottlenecks that limit production rate increases.

b) (40 points) Draw a proposed future state VSM for Castellon. In your future state VSM, assume production to a finished goods supermarket having packed cases, 20 product variations. Consider:

• Castellon already has continuous flow through tile-pressing, glazing and firing; where else can you use continuous flow?
• Are there any other places where supermarket pull systems are needed?
• At what point will you schedule production (i.e., where is the pacemaker)?
• How will you level the production mix, i.e., how will you handle the critical changeovers?
• What increment of work (i.e., pitch quantity) will you use at the pacemaker?
• What process improvements (kaizen) are necessary for the value stream to flow as specified by your future-state design?

Dry-route granulation details:

• The proposed dry process has gravimetric feeders suppling raw material powder to the milling/granulation process; feeders can run in either batch-endpoint or continuous rate mode.
• The mill breaks up any lumps or agglomerates of powder. It has a residence time of a few seconds; you can assume it is instantaneous.
• The mixer granulator in this process adds a relatively small amount of aqueous binder form granules suitable for dry-pressing. In batch mode, the cycle time is about 20 minutes. In continuous, the mean residence time is about 5 minutes.
• The output of the granulator is screened to remove any oversize granules which are recycled through the mill. Recycle is about 20%.
• Granules are conditioned to a target moisture in a continuous fluidized bed; optimizing plasticity of granules for compaction. The fluid bed uses heat recycled from the continuous kiln, operating continuously with a mean residence time of about 20 minutes.
• The process requires 1 attendant to monitor recycles and adjust process controls.
• Washout changeover of the dry-route granulation is assumed to be comparable with the current wet process, i.e., average C/O = 2 hours.

3) (20 points) Castellon wants to reduce the lead time for customers' orders and increase their annual inventory turns.In addition to the new dry-granulation process, include two additional features in your Future State VSM that can significantly address this. Identify these two features and quantify their benefit in terms of lead-time reduction.

4) (10 points) Anticipating growth in their business, Castellon wants to be able to increase its overall production capacity. Analyze and suggest opportunities to increase production. What is the practical maximum associated with your proposal?

5) (10 points, extra credit) Business is great! If Castellon goes to a 7-day 3-shift schedule for tile making, what is the upper limit on the capacity according to your future state VSM?Describe kaizen needed.

[1] A. Mezquita et al, "How to reduce energy and water consumption in the preparation of raw materials for ceramic tile manufacturing: Dry versus wet route," Journal of Cleaner Production (2017). See "Granules for ceramic tile" in BS supplement.